Coated metal sheet, method for manufacturing same, and exterior building material

ABSTRACT

Provided is a coated metal sheet for exterior use, having a metal sheet, and a top coat film situated on the metal sheet. The top coat film contains 0.2-15 volume percent of a gloss control agent composed of porous particles and a delustering agent composed of primary particles. The coated metal sheet satisfies the following expressions in which, in the number-size distribution of the gloss control agent and the delustering agent, R is the number-average particle diameter (μm) of the gloss control agent, D1 97.5  and D2 97.5  are 97.5% particle diameter values (μm) of the gloss control agent and the delustering agent, Ru is the upper limit particle diameter (μm) of the gloss control agent, and T is the film thickness (μm) of the top coat film. 
         D 1 97.5   /T ≦0.7
 
         Ru ≦1.2 T  
 
         R ≧1.0
 
       2.0≦ D 2 97.5   /T ≦7.0
 
       13≦ T ≦20.

TECHNICAL FIELD

The present invention relates to a coated metal sheet for exterior use, a production method therefor, and an exterior building material.

BACKGROUND ART

Coated metal sheets, excellent in versatility, designability, durability and the like, have been used in various applications. In coated metal sheets for exterior building material applications, mainly from the viewpoint of designability, a gloss adjusting agent is usually blended in an overcoat coating film which is a surface of the coated metal sheet surface. Silica particles are usually used as the above-described gloss adjusting agent in the coated metal sheets for exterior building materials. The particle diameter of the silica particles is usually specified by an average particle diameter. The average particle diameter of the silica particles as the gloss adjusting agent in the coated metal sheet is usually from 3 to 30 μm, depending on the color and the application (for example, see PTL 1 (paragraph 0018)). Additionally, in order to provide the coating film with unevenness to thereby provide the appearance and texture of a so-called “matte coated steel sheet”, it is necessary to further add a matting agent having a particle diameter larger than that of the gloss adjusting agent. Examples of the type of the matting agent include glass beads, resin beads and the like. The average particle diameter of the matting agent is usually from 10 to 50 μm (for example, see PTL 2 (paragraph 0016)).

CITATION LIST Patent Literature PTL 1

-   Japanese Patent Application Laid-Open No. 2011-148107

PTL 2

-   Japanese Patent Application Laid-Open No. 2004-154993

SUMMARY OF INVENTION Technical Problem

As coated metal sheets for exterior building materials, chromate-coated steel sheets are used. Efforts have been made to improve the molding processability or the corrosion resistance at cut ends for the chromate-coated steel sheets, which thus have had long-term durability. Meanwhile, strong interest has been shown to environmental preservation in recent years also in the technical field of exterior building materials. Accordingly, legal regulations to ban the use of components that adversely affect or cause a concern about possibility of adversely affecting the environment have been under consideration. For example, restriction of the use of hexavalent chromium components, generally used in coated metal sheets as an anti-rust component, in the near future is under consideration. Also for chromate-free coated steel sheets, various considerations have been made such as pre-coating treatment, optimization of anti-rust pigments and the like, and characteristics obtained at molding processed portions and cut ends are comparable to those of the chromate-coated steel sheets.

However, the corrosion resistance of the flat portion in chromate-coated steel sheets did not lead to a large problem, while corrosion in the flat portion in chromate-free coated steel sheets may become severe. Particularly when silica particles are used as the above-described gloss adjusting agent, corrosion such as stain rust, coating film blistering and the like, in the flat portion has occurred during actual use in some cases, before the intended age of service, as shown in FIG. 1.

An object of the present invention is to provide a coated metal sheet and an exterior building material that have matte designability as well as, even being chromate-free, have excellent flat-portion corrosion resistance equivalent to or greater than that of coated metal sheets comprising a chromate anti-rust treated metal sheet.

Solution to Problem

The present inventors have intensively studied causes of the aforementioned corrosion in the flat portion. FIG. 2 is a micrograph of a corroded portion in the flat portion of a chromate-free coated metal sheet. In FIG. 2, portion A is a portion where silica particles as a gloss adjusting agent are exposed from the overcoat coating film, and portion B is a portion where the silica particles have fallen off from the overcoat coating film. FIG. 3 is a reflection electron micrograph of a cross section along line L, in FIG. 2, in portion A of the above-described coated metal sheet. FIG. 4 is a reflection electron micrograph of a cross section along line L, in FIG. 2, in portion B of the above-described coated metal sheet. FIG. 3 clearly shows the occurrence of cracks at the silica particles exposed on the surface of the overcoat coating film, and FIG. 4 clearly shows that corrosion of the metal sheet originates from the holes in the overcoat coating film from which the silica particles have fallen off.

As described above, the present inventors have confirmed that, when particles having micropores such as silica are used as the gloss adjusting agent, the corrosion occurs in a portion where the gloss adjusting agent in the overcoat coating film has cracked, collapsed, or fallen off, and also that the gloss adjusting agent exposed from the overcoat coating film to be worn in actual use cracks, collapses and falls off from the overcoat coating film.

The present inventors have also investigated the gloss adjusting agent to thereby confirm that the silica particles specified by an average particle diameter contain particles considerably larger than the average particle diameter relative to the thickness of the overcoat coating film. For example, when observing, among commercially available silica particles to be used as the above-described gloss adjusting agent, silica particles having an average particle diameter of 3.3 μm with an electron microscope, the present inventors have confirmed that silica particles having a particle diameter of about 15 μm are contained (FIG. 5). Additionally, the present inventors have observed the surface of the silica particles (portion B in FIG. 6A) and have confirmed that numberless minute gaps, which are specific to aggregated particles, are open to the surface (FIG. 6B).

Similarly when aggregated particles such as silica, polyacrylonitrile (PAN) and the like are used as a matting agent to be additionally used in the overcoat coating film, the present inventors have also confirmed that corrosion originates in a portion where the matting agent exposed from the overcoat coating film has cracked, collapsed, or fallen off (FIG. 7 and FIG. 8).

Then, the present inventors, focusing on the fact that such aggregated particles having a large particle diameter decrease the corrosion resistance, have found that, by use of a gloss adjusting agent having a specific particle diameter relative to the thickness of the overcoat coating film and a matting agent, corrosion resistance can be obtained equivalent to or greater than the corrosion resistance achieved by chromate-based chemical conversion treatment and by use of a chromium-containing anti-rust pigment in an undercoat coating film in conventional metal sheets, having completed the present invention.

Thus, the present invention relates to a coated metal sheet and an exterior building material below.

[1] A coated metal sheet including: a metal sheet, and an overcoat coating film to be disposed on the metal sheet, in which the overcoat coating film comprises a gloss adjusting agent which is particles having micropores and a matting agent which is primary particles, in which a content of the gloss adjusting agent in the overcoat coating film is from 0.2 to 15 vol %, in which a content of the matting agent in the overcoat coating film is from 0.2 to 15 vol %, and in which the coated metal sheet satisfies the following equations:

D1_(97.5) /T≦0.7

Ru≦1.2T

R≧1.0

2.0≦D2_(97.5) /T≦7.0

13≦T≦20

in which R (μm) is a number average particle diameter of the gloss adjusting agent, T (μm) is a film thickness of the overcoat coating film, D1_(97.5) (μm) is a 97.5% particle diameter in an accumulated particle size distribution of the gloss adjusting agent based on the number of particles, D2_(97.5) (μm) is a 97.5% particle diameter in an accumulated particle size distribution of the matting agent based on the number of particles, and Ru (μm) is an upper limit particle diameter in a number particle size distribution of the gloss adjusting agent. [2] A coated metal sheet including: a metal sheet, an intercoat coating film to be disposed on the metal sheet, and an overcoat coating film to be disposed on the intercoat coating film, in which the overcoat coating film comprises a gloss adjusting agent which is particles having micropores and a matting agent which is primary particles, in which a content of the gloss adjusting agent in the overcoat coating film is from 0.01 to 15 vol %, in which a content of the matting agent in the overcoat coating film is from 0.01 to 15 vol %, and in which the coated metal sheet satisfies the following equations:

D1_(97.5) /T≦0.7

Ru≦1.2T

R≧1.0

0.5≦D2_(97.5) /T≦7.0

3≦T≦20

in which R (μm) is a number average particle diameter of the gloss adjusting agent, T (μm) is a film thickness of the overcoat coating film, D1_(97.5) (μm) is a 97.5% particle diameter in an accumulated particle size distribution of the gloss adjusting agent based on the number of particles, D2_(97.5) (μm) is a 97.5% particle diameter in an accumulated particle size distribution of the matting agent based on the number of particles, and Ru (μm) is an upper limit particle diameter in a number particle size distribution of the gloss adjusting agent. [3] The coated metal sheet according to [1], further including an undercoat coating film between the metal sheet and the overcoat coating film. [4] The coated metal sheet according to [2], further including an undercoat coating film between the metal sheet and the intercoat coating film. [5] The coated metal sheet according to any one of [1] to [4], in which the Ru is less than T. [6] The coated metal sheet according to any one of [1] to [5], in which the metal sheet has been subjected to non-chromate anti-rust treatment, and the coated metal sheet is chromate-free. [7] The coated metal sheet according to any one of [1] to [5], in which the metal sheet has been subjected to chromate anti-rust treatment. [8] The coated metal sheet according to any one of [1] to [7], in which the gloss adjusting agent is silica particles. [9] The coated metal sheet according to in any one of [1] to [8], having a glossiness at 75° is 1 to 25. [10] The coated metal sheet according to in any one of [1] to [9], being a coated metal sheet for exterior use. [11] An exterior building material composed of the coated metal sheet according to any one of [1] to [9].

Also, the present invention relates to a method for producing a coated metal sheet below.

[12] A method for producing a coated metal sheet having a metal sheet and an overcoat coating film to be disposed on the metal sheet, including the steps of: applying an overcoat coating material containing a resin, a gloss adjusting agent, and a matting agent onto the metal sheet, and curing the coating film of the overcoat coating material to form the overcoat coating film, in which a content of the gloss adjusting agent in the overcoat coating film is from 0.2 to 15 vol %, and a content of the matting agent in the overcoat coating film is from 0.2 to 15 vol %, in which the gloss adjusting agent is particles having micropores, and the matting agent is primary particles, and in which the gloss adjusting agent and the matting agent which satisfy the following equations are employed:

D1_(97.5) /T≦0.7

Ru≦1.2T

R≧1.0

2.0≦D2_(97.5) /T≦7.0

13≦T≦20

in which R (μm) is a number average particle diameter of the gloss adjusting agent, T (μm) is a film thickness of the overcoat coating film, D1_(97.5) (μm) is a 97.5% particle diameter in an accumulated particle size distribution of the gloss adjusting agent based on the number of particles, D2_(97.5) (μm) is a 97.5% particle diameter in an accumulated particle size distribution of the matting agent based on the number of particles, and Ru (μm) is an upper limit particle diameter in a number particle size distribution of the gloss adjusting agent. [13] A method for producing a coated metal sheet having a metal sheet and an overcoat coating film to be disposed on the metal sheet, including the steps of: applying an overcoat coating material containing a resin, a gloss adjusting agent, and a matting agent onto the metal sheet; and curing the coating film of the overcoat coating material to form the overcoat coating film; in which a content of the gloss adjusting agent in the overcoat coating film is from 0.01 to 15 vol %, and a content of the matting agent in the overcoat coating film is from 0.01 to 15 vol %, in which the gloss adjusting agent is particles having micropores, and the matting agent is primary particles, and in which the gloss adjusting agent and the matting agent which satisfy the following equations are employed:

D1_(97.5) /T≦0.7

Ru≦1.2T

R≧1.0

0.5≦D2_(97.5) /T≦7.0

3≦T≦20

in which R (μm) is a number average particle diameter of the gloss adjusting agent, T (μm) is a film thickness of the overcoat coating film, D1_(97.5) (μm) is a 97.5% particle diameter in an accumulated particle size distribution of the gloss adjusting agent based on the number of particles, D2_(97.5) (μm) is a 97.5% particle diameter in an accumulated particle size distribution of the matting agent based on the number of particles, and Ru (μm) is an upper limit particle diameter in a number particle size distribution of the gloss adjusting agent. [14] The method for producing a coated metal sheet according to [12] or [13], in which the overcoat coating material has been subjected to treatment for pulverizing the particles in the overcoat coating material.

Advantageous Effects of Invention

The present invention prevents exposure, cracking and the like of the gloss adjusting agent, and cracking, fall-off and the like of the matting agent, at the intended age of service. As a result, there is provided a coated metal sheet that has intended matte designability having an adjusted gloss as well as, although being chromate-free, has excellent flat-portion corrosion resistance equivalent to or greater than that of coated metal sheets comprising a chromate anti-rust treated metal sheet.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a micrograph of a corroded portion (coating film blistering) occurring in the flat portion of a chromate-free coated metal sheet in actual use of five years;

FIG. 2 is a micrograph of a corroded portion in the flat portion of the chromate-free coated metal sheet;

FIG. 3 is a reflection electron micrograph of a cross section along line L, in FIG. 2, in portion A of the coated metal sheet shown in FIG. 2;

FIG. 4 is a reflection electron micrograph of a cross section along line L, in FIG. 2, in portion B of the coated metal sheet shown in FIG. 2;

FIG. 5 is an electron micrograph of commercially available silica particles having an average particle diameter of 3.3 μm;

FIG. 6A is an electron micrograph of commercially available silica particles, and FIG. 6B is an enlarged electron micrograph of portion B in FIG. 6A;

FIG. 7 is a micrograph of a cross section of a corroded portion in the flat portion of a chromate-free coated metal sheet in which silica particles are used as a matting agent; and

FIG. 8 is a micrograph of a cross section of a corroded portion in the flat portion of a chromate-free coated metal sheet in which PAN particles are used as a matting agent.

DESCRIPTION OF EMBODIMENTS

Hereinafter, the coated metal sheet according to one embodiment of the present invention will be described. The above-described coated metal sheet includes a metal sheet and an overcoat coating film to be disposed on/above the metal sheet.

The above-described metal sheet can be selected from known metal sheets in the range where the effect of the present embodiment can be achieved. Examples of the metal sheet include cold-rolled steel sheets, galvanized steel sheets, Zn—Al alloy-plated steel sheet, Zn—Al—Mg alloy-plated steel sheets, aluminum-plated steel sheets, stainless steel sheets (including austenitic, martensitic, ferritic, and ferrite-martensite two-phase systems), aluminum sheets, aluminum-alloy sheets, copper sheets and the like. The above-described metal sheets are preferably plated steel sheets from the viewpoint of corrosion resistance, lighter weight, and cost-effectiveness. The plated steel sheet is preferably hot-dip 55% Al—Zn alloy-plated steel sheets, Zn—Al—Mg alloy-plated steel sheets, or aluminum-plated steel sheets, particularly from the viewpoint of corrosion resistance and from the viewpoint of suitability for exterior building materials.

The above-described metal sheet preferably has a chemical conversion film on its surface, from the viewpoint of improving the adhesiveness of the coated metal sheet and the corrosion resistance. Chemical conversion is one type of pre-coating treatment for metal sheets, and a chemical conversion film is a composition layer formed by the pre-coating treatment. The above-described metal sheets are preferred in that the sheets have been subjected to non-chromate anti-rust treatment from the viewpoint of reducing environmental loads in production and use of the coated metal sheet, and in that the sheets have been subjected to chromate anti-rust treatment from the viewpoint of further improving the corrosion resistance.

Examples of the above-described chemical conversion film by the above-described non-chromate anti-rust treatment include Ti—Mo composite films, fluoro acid-based films, phosphate films, resin-based films, resin and silane-coupling-agent-based films, silica-based films, silica and silane-coupling-agent-based films, zirconium-based films, and zirconium and silane-coupling-agent-based films.

From the above-described viewpoint, the amount of the Ti—Mo composite film deposited is preferably 10 to 500 mg/m² in terms of total Ti and Mo, the amount of the fluoro acid film deposited is preferably 3 to 100 mg/m² in terms of fluorine or in terms of total elemental metals, and the amount of the phosphate film deposited is preferably 0.1 to 5 g/m² in terms of elemental phosphorous, in the above-described metal sheet.

The amount of the above-described resin-based film deposited is preferably 1 to 500 mg/m² in terms of the resin, the amount of the above-described resin and silane coupling agent-based film deposited is preferably 0.1 to 50 mg/m² in terms of Si, the amount of the above-described silica-based film deposited is preferably 0.1 to 200 mg/m² in terms of Si, the amount of the above-described silica and silane coupling agent-based film deposited is preferably 0.1 to 200 mg/m² in terms of Si, the amount of the above-described zirconium-based film deposited is preferably 0.1 to 100 mg/m² in terms of Zr, and the amount of the above-described zirconium and silane coupling agent-based film deposited is preferably is 0.1 to 100 mg/m² in terms of Zr.

Also, examples of the above-described chromate anti-rust treatment include coating-type chromate treatment and phosphate-chromate-based treatment. From the above-described viewpoint, the amount of the film deposited by the chromate anti-rust treatment in the above-described metal sheet is preferably from 20 to 80 g/m² in terms of element chromium.

The above-described overcoat coating film is usually composed of resin other than fluorine resin. The resin is selected as appropriate from the viewpoint of designability, weather resistance and the like. Examples of the resin include polyester, acrylic resins, and urethane resins.

The film thickness T of the above-described overcoat coating film is from 13 to 20 μm. An extremely large film thickness T of the overcoat coating film may be responsible for occurrence of defective coating (foaming), reduction in the productivity, increase in the production cost and the like, whereas, with an extremely small film thickness T, the intended designability and the intended flat portion-corrosion resistance may not be achieved. For example, in order to obtain a coated metal sheet that has good productivity, exhibits the intended gloss and coloring, and can be actually used as an exterior building material for at least 10 years, the film thickness T of the overcoat coating film is, for example, preferably 14 μm or more, more preferably 15 μm or more, from the above-described viewpoint. Also due to the above-described reason, the film thickness T of the overcoat coating film is preferably 19 μm or less, more preferably 18 μm or less. The film thickness T of the overcoat coating film is, for example, the average value of distances from the bottom to the surface at a plurality of positions on a portion where the matting agent of the overcoat coating film is not present.

Alternatively, when the coated metal sheet has other coated film(s) other than the overcoat coating film, the film thickness T of the overcoat coating film can be determined in further consideration of the other coated film(s). For example, when the coated metal sheet has an undercoat coating film described below and the overcoat coating film, the film thickness T of the overcoat coating film is preferably from 14 to 20 μm from the viewpoint of the designability, corrosion resistance, and processability. Alternatively, when the coated metal sheet has an undercoat coating film, an intercoat coating film described below, and the overcoat coating film, the film thickness T of the overcoat coating film is from 3 to 20 μm. Additionally, from the above-described viewpoint, the film thickness T is preferably from 4.0 to 19 μm, more preferably from 5.0 to 18 μm.

The film thickness T of the above-described overcoat coating film is, from the viewpoint of the designability of the coated metal sheet, preferably larger when a color of the overcoat coating film is light, and can be smaller when the color of the overcoat coating film is dark. Although it depends on the case, for example, when the value L of the overcoat coating film is 80 or less, the film thickness T of the overcoat coating film can be 15 μm or less, and when the value L of the overcoat coating film is more than 80, the film thickness is preferably more than 15 μm.

Alternatively, the film thickness T of the above-described overcoat coating film can be smaller, as the color of the overcoat coating film is closer to the color of the surface of the steel sheet before the overcoat coating film is formed (for example, an undercoat coating film and an intercoat coating film described below), from the viewpoint of the designability of the coated metal sheet. Although it depends on the case, for example, when the absolute value ΔL of the difference between the value L of the overcoat coating film and the value L of the color of the surface of the steel sheet before the coating film is formed is 10 or less, the film thickness T of the overcoat coating film can be 13 μm or less, when ΔL is 20 or less, the film thickness T can be 15 μm or less, and when ΔL is 50 or less, the film thickness T can be 17 μm or less.

Also, in the coated metal sheet according to the present embodiment, even an overcoat coating film in a coated metal sheet that has no intercoat coating film can be formed similarly as an overcoat coating film in a coated metal sheet having an intercoat coating film. For example, when the color of the overcoat coating film is close to that of its base (for example, an undercoat coating film) (for example, ΔL is 10 or less), when the color of the overcoat coating film is a dark color (for example, the value L is 25 or less) or the like, the film thickness T of the overcoat coating film can be reduced to be equivalent to the film thickness of the overcoat coating film in a coated metal sheet having an intercoat coating film (for example, down to 3 μm).

Incidentally, the above-described value L can be determined by calculation by the Hunter's color difference formula from the measurement result by a commercially available spectrophotometer (for example, manufactured by KONICA MINOLTA OPTICS, INC. “CM3700d”).

The above-described overcoat coating film contains a gloss adjusting agent. The gloss adjusting agent is blended in the overcoat coating film to moderately roughen the surface of the overcoat coating film for the purpose to achieve the intended gloss in the coated metal sheet, for the purpose to adjust variation of gloss among production lots and the like, imparting the intended appearance with gloss to the coated metal sheet.

The above-described gloss adjusting agent has a number average particle diameter R (hereinafter, may be also referred to as “R1”) of 1.0 μm or more. When the gloss adjusting agent is extremely small, the gloss of the overcoat coating film is extremely high, and thus, the intended designability may not be achieved. As such, it is possible to determine the number average particle diameter of the gloss adjusting agent R1 as appropriate depending on the intended designability (glossiness) of the coated metal sheet in the range where R1 satisfies the formula described below. However, when R1 is extremely large, the roughness of the overcoat coating film increases, and thus the intended designability cannot be achieved. For example, from the viewpoint of obtaining a coated metal sheet having a glossiness at 75° of 1 to 25 in addition to flat-portion corrosion resistance, the number average particle diameter R1 of the gloss adjusting agent is preferably 2.0 μm or more, more preferably 3.0 μm or more, still more preferably 5.0 μm or more, or even preferably 7.0 μm or more. The number average particle diameter can be confirmed by observation of the cross-section of the overcoat coating film or can be measured by an image analyzing method and the Coulter method (for example, using an accurate particle sizing and counting analyzer “Multisizer 4” manufactured by Beckman Coulter Inc.).

Alternatively, when the coated metal sheet has other coated film(s) other than the overcoat coating film, the number average particle diameter R1 of the above-described gloss adjusting agent can be determined depending on the film thickness T of the overcoat coating film. For example, when the coated metal sheet has an undercoat coating film and an overcoat coating film, the number average particle diameter R1 of the above-described gloss adjusting agent is preferably 2.0 μm or more, from the viewpoint of the designability by the intended gloss, corrosion resistance, and processability. Alternatively, when the coated metal sheet has an undercoat coating film, an intercoat coating film described below, and an overcoat coating film, the number average particle diameter R1 of the above-described gloss adjusting agent is 1.0 μm or more. Additionally, from the above-described viewpoint, the number average particle diameter R1 is preferably 2.0 μm or more.

The content of the above-described gloss adjusting agent in the above-described overcoat coating film is 0.2 to 15 vol %. When the content is extremely high, the gloss of the overcoat coating film becomes extremely low, and also, the processed-part adhesiveness decreases. When the content is extremely low, the gloss may not be controlled. Thus, even if the content is extremely large or small, the intended designability may not be achieved. For example, from the viewpoint of obtaining a coated metal sheet having a glossiness at 75° of 1 to 25, the content of the gloss adjusting agent in the overcoat coating film is preferably 0.4 vol % or more, more preferably 0.6 vol % or more. Also from the above-described reason, the content of the gloss adjusting agent in the overcoat coating film is preferably 13 vol % or less, more preferably 11 vol % or less. The content can be confirmed by measurement of the ash content in the overcoat coating film, collection of the gloss adjusting agent by dissolution of the overcoat coating film, image analysis of a cross-sectional image of element discrimination conducted at a plurality of points or the like.

Alternatively, when the coated metal sheet has other coated film(s) other than the overcoat coating film, the content of the above-described gloss adjusting agent can be determined in further consideration of the presence of the other coating film(s). For example, when the coated metal sheet has an undercoat coating film described below and the overcoat coating film, the content of the gloss adjusting agent is preferably from 0.4 to 15 vol % from the viewpoint of the designability, corrosion resistance, and processability. Alternatively, when the coated metal sheet has an undercoat coating film, an intercoat coating film described below, and the overcoat coating film, the content of the gloss adjusting agent is from 0.01 to 15 vol %. Additionally, from the above-described viewpoint, the content is preferably from 0.1 to 13 vol %, more preferably 0.2 to 11 vol %.

The above-described gloss adjusting agent is particles having micropores (hereinafter, may be referred to as “microporous particles”). Examples of the microporous particles include aggregates formed by chemical bonding of primary particles, agglomerates formed by physical bonding of primary particles, and porous particles. The porous particles have a porous structure at least inside the particles. The above-described gloss adjusting agent may be composed solely of the above-described microporous particles or may contain particles other than microporous particles. The microporous particles may be inorganic particles or organic particles, and can be selected from known microporous particles used as a gloss adjusting agent, in the range where the particles satisfy the equation described below. Examples of the materials of the microporous particles include silica, calcium carbonate, barium sulfate, polyacrylonitrile, and calcium carbonate-calcium phosphate composites. The above-described gloss adjusting agent is preferably silica particles from the viewpoint of having a high function of adjusting the gloss of coated metal sheets.

The above-described coated metal sheet satisfies the following equation:

D1_(97.5) /T≦0.7

wherein R1 is the number average particle diameter of the above-described gloss adjusting agent (μm), T is the film thickness of the above-described overcoat coating film (μm), and D1_(97.5) is the 97.5% particle diameter (μm) in the accumulated particle size distribution of the above-described gloss adjusting agent based on the number of particles (hereinafter, may also be referred to as “number particle size distribution”). However, when the upper particle size of the number particle size distribution of the gloss adjusting agent is set to Ru (μm), the corresponding Ru is 1.2T or less. “Upper limit particle diameter (Ru)” is a particle diameter when the particle size distribution curve in the number particle size distribution meets the baseline at the number average particle diameter R1 or more.

D1_(97.5) will be a substantial index of the particle diameter of the above-described gloss adjusting agent by which the effect of the present invention is achieved. With extremely large D1_(97.5)/T, the above-described microporous particles may be exposed due to wearing of the overcoat coating film during actual use, and the intended flat portion-corrosion resistance may not be achieved. With extremely small D1_(97.5)/T, the intended glossiness may not be achieved.

For example, from the viewpoint of obtaining a coated metal sheet having a glossiness at 75° of 1 to 25, D1_(97.5)/T is preferably 0.3 or more, more preferably 0.4 or more. Additionally, from the viewpoint of obtaining a coated metal sheet having an actual age of service as an exterior building material of at least 10 years or more, D1_(97.5)/T is preferably 0.6 or less, more preferably 0.5 or less.

Meanwhile, in the corresponding number particle size distribution, the content of the particles larger than D1_(97.5) is only about 2.5% based on the number of all the particles. Thus, a gloss adjusting agent of which particle size distribution curve exhibits specific sharpness at a particle diameter of the number average particle diameter R1 or more in the number particle size distribution, satisfying “D1_(97.5)/T≦0.7”, can be applied as it is to the present invention. In other words, the above-described gloss adjusting agent having a meeting point (Ru) of 1.2T or less, at which the particle size distribution curve in the number particle size distribution meets the baseline of the number particle size distribution at the number average particle diameter R1 or more, which satisfies “D1_(97.5)/T≦0.7”, can be applied to the present invention.

The reason why sufficient flat portion-corrosion resistance is exhibited even when the upper limit particle diameter Ru (μm) is 1.2T or less (even when more than 0.7T) can be assumed as follows. First, in the overcoat coating film, the resin composition of the overcoat coating film is superposed on the gloss adjusting agent, and thus, it is conceivable that a gloss adjusting agent having a particle diameter of 1.2T or less normally may not be exposed from the surface of the overcoat coating film. Alternatively, particles having a particle diameter larger than 0.7T in the above-described gloss adjusting agent are unlikely to deviate from the normal distribution so significantly, even if the actual number particle size distribution described above in the range larger than the above-described R1 deviates from the normal distribution. Thus, it is conceivable that the content of the particles will be less than 2.5% at most based on the total. Therefore, it is conceivable that particles having a particle diameter larger than 0.7T in the above-described gloss adjusting agent may be too small in number to substantially influence the flat portion-corrosion resistance. Moreover, the above-described gloss adjusting agent is oddly shaped in general, and usually low-profile to some extent. Conceivably, in the above-described gloss adjusting agent in the overcoat coating film, usually the longitudinal direction of the gloss adjusting agent tends to be oriented to the horizontal direction more than the vertical direction due to the application of the overcoat coating material described below, and thus, the particle diameter in the in film-thickness direction in the above-described gloss adjusting agent in the overcoat coating film usually becomes shorter than the long diameter of the gloss adjusting agent (for example, 1.2T).

When the above-described Ru is extremely large, the above-described microporous particles are exposed due to wearing of the overcoat coating film during actual use, and the intended flat portion-corrosion resistance may not be obtained. From the viewpoint of obtaining a coated metal sheet having an actual age of service as an exterior building material of at least 10 years or more, Ru is preferably less than T, more preferably 0.7T or less, still more preferably 0.6T or less. R1, D1_(97.5), and Ru can be determined from the number particle size distribution of the above-described gloss adjusting agent.

Incidentally, the side smaller than the average particle diameter R1 in the number particle size distribution of the above-described gloss adjusting agent may be in any mode as long as the conditions of the above-described particle size distribution are satisfied.

As the above-described gloss adjusting agent that satisfies the conditions according to the above-described particle size distribution, commercially-available products and their classified materials can be used.

Incidentally, to produce above-described coated metal sheet, the above-described gloss adjusting agent may not satisfy the particle size conditions aforementioned (for example, coarse particles larger than 1.2T are present and the like), or may deviate from the above-described conditions in the process of production. In this case, a step of pulverizing the coarse particles in the overcoat coating material described below, such as roller mill treatment as described below, is suitably performed from the viewpoint of obtaining the above-described coated metal sheet.

The above-described overcoat coating film also contain a matting agent. The above-described matting agent is blended to the overcoat coating film in order to exhibit unevenness that is larger than the coarseness to be imparted by a gloss adjusting agent to the overcoat coating film and can be visually confirmed and to impart a texture, providing the coated metal sheet with the intended appearance. The matting agent also includes those having a particle diameter larger than the film thickness of the overcoat coating film, and thus can prevent the overcoat coating film from being scratched. Thereby, the scratch resistance of the coated metal sheet can be improved.

Although the number average particle diameter of the above-described matting agent (hereinafter, may be also referred to as “R2”) is not particularly limited, the matting agent having an extremely small particle diameter cannot reduce the gloss of the overcoat coating film, and the intended designability may not be achieved. It is possible to determine the number average particle diameter of the matting agent R2 as appropriate depending on the intended designability (glossiness) of the coated metal sheet in the range where R2 satisfies the equation described below. However, when R2 is extremely large, the matting agent causes streaks on coating, and the intended designability may not be achieved. For example, to obtain a coated metal sheet having a glossiness at 75° of 1 to 25 in addition to flat-portion corrosion resistance, the number average particle diameter R2 of the matting agent is preferably 5.0 μm or more, more preferably 10.0 μm or more, still more preferably 15.0 μm or more, even more preferably 20 μm or more, still even more preferably 25 μm or more. Also, due to the above-described reason, the number average particle diameter of the matting agent R2 is preferably 75 μm or less, more preferably 50 μm or less, still more preferably 40 μm or less. The number average particle diameter can be confirmed by observation of the cross-section of the overcoat coating film or can be measured by an image analyzing method and the Coulter method (for example, using an accurate particle sizing and counting analyzer “Multisizer 4” manufactured by Beckman Coulter Inc.).

The content of the above-described matting agent in the above-described overcoat coating film is 0.2 to 15 vol %. When the content is extremely high, the gloss of the overcoat coating film decreases, and also, the processed-part adhesiveness decreases. In contrast, when the content is extremely low, gloss cannot be adjusted, and in both cases, the intended designability may not be achieved. For example, from the viewpoint of obtaining a coated metal sheet having a glossiness at 75° of 1 to 25, the content of the matting agent in the overcoat coating film is preferably 0.4 vol % or more, more preferably 0.6 vol % or more. Also due to the above-described reason, the content of the matting agent in the overcoat coating film is preferably 13 vol % or less, more preferably 10 vol % or less. The content can be confirmed by measurement of the ash content in the overcoat coating film, collection of the matting agent by dissolution of the overcoat coating film, image analysis of a cross-sectional image of element discrimination conducted at a plurality of points or the like.

Alternatively, when the coated metal sheet has other coated film(s) other than the overcoat coating film, the content of the above-described matting agent can be determined in further consideration of the presence of the other coated film(s). For example, when the coated metal sheet has an undercoat coating film described below and the overcoat coating film, the content of the matting agent is preferably from 0.4 to 15 vol % from the viewpoint of the designability, corrosion resistance, and processability. Alternatively, when the coated metal sheet has the undercoat coating film, an intercoat coating film described below, and the overcoat coating film, the content of the matting agent is from 0.01 to 15 vol %. Additionally, from the above-described viewpoint, the content is preferably from 0.1 to 13 vol %, more preferably 0.2 to 11 vol %.

The above-described matting agent is primary particles. The primary particles refer to particles having no micropores that may cause the particles to collapse when the substance (for example, water) present in their voids expands. The primary particles may be resin particles or inorganic particles, and can be selected from known primary particles used as a matting agent, in the range where the particles satisfy the equation described below. Specific examples of the primary particles include primary particles composed of resin such as acrylic resin, polyurethane resin, polyester resin, melamine resin, urea resin, polyamide resin and the like (resin particles); and primary particles composed of an inorganic compound such as glass, silicon carbide, boron nitride, zirconia, alumina, silica, and the like (inorganic particles). The shape of these primary particles is preferably approximately spherical, but may be other shape such as a cylindrical shape, a disc shape and the like. Also, recesses and the like may be present on the surface of the primary particles unless they are micropores that may become an origin of collapse of the particles.

The above-described coated metal sheet satisfies the following equation:

2.0≦D2_(97.5) /T≦7.0

wherein T (μm) is the film thickness of the above-described overcoat coating film, and D2_(97.5) is the 97.5% particle diameter (μm) in the accumulated particle size distribution of the above-described matting agent based on the number of particles.

D2_(97.5) will be a substantial index of the particle diameter of the above-described matting agent by which the effect of the present invention is achieved. When D2_(97.5)/T is extremely large, streaks or the like attributable to the matting agent occur on coating of the overcoat coating film, and a fair coating appearance may not be achieved. When D2_(97.5)/T is extremely small, the intended texture may not be achieved.

For example, from the viewpoint of obtaining a coated metal sheet having a glossiness at 75° of 1 to 25, D2_(97.5)/T is preferably 3 or more, more preferably 4 or more. Additionally, for example, from the viewpoint of obtaining a coated metal sheet having an actual age of service as an exterior building material of at least 10 years or more, D2_(97.5)/T is preferably 6 or less, more preferably 5 or less. R2 and D2_(97.5) can be determined from the number particle size distribution of the above-described matting agent.

Alternatively, when the coated metal sheet has other coated film(s) other than the overcoat coating film, D2_(97.5)/T can be determined in further consideration of the other coated film(s). For example, when the coated metal sheet has an undercoat coating film described below and the overcoat coating film, D2_(97.5)/T is preferably from 3.0 to 7.0 from the viewpoint of the designability, corrosion resistance, and processability. Alternatively, when the coated metal sheet has the undercoat coating film, an intercoat coating film described below, and the overcoat coating film, D2_(97.5)/T is from 0.5 to 7.0. Additionally, from the above-described viewpoint, D2_(97.5)/T is preferably from 1.0 to 6.0, more preferably from 2.0 to 5.0.

The above-described overcoat coating film may further contain other ingredients besides the resin, gloss adjusting agent, and matting agent aforementioned, in the range where the effect of the present embodiment can be achieved. For example, the overcoat coating film may further contain a colorant. Examples of the colorant include inorganic pigments such as titanium oxide, calcium carbonate, carbon black, iron black, iron oxide yellow, titanium yellow, colcothar, iron blue, cobalt blue, cerulean blue, ultramarine blue, cobalt green, molybdenum red and the like; composite oxide calcined pigments containing metal components such as CoAl, CoCrAl, CoCrZnMgAl, CoNiZnTi, CoCrZnTi, NiSbTi, CrSbTi, FeCrZnNi, MnSbTi, FeCr, FeCrNi, FeNi, FeCrNiMn, CoCr, Mn, Co, SnZnTi and the like; metallic pigments such as Al flakes, resin-coated Al flakes, Ni flakes, stainless flakes and the like; and organic pigments such as Quinacridone Red, Lithol Red B, Brilliant Scarlet G, Pigment Scarlet 3B, Brilliant Carmine 6B, Lake Red C, Lake Red D, Permanent Red 4R, Bordeaux 10B, Fast Yellow G, Fast Yellow 10G, Pare Red, Watching Red, Benzidine Yellow, Benzidine Orange, Bon Maroon L, Bon Maroon M, Brilliant Fast Scarlet, Vermilion Red, Phthalocyanine Blue, Phthalocyanine Green, Fast Skyblue, Aniline Black and the like. The above-described colorant is sufficiently smaller relative to the above-described gloss adjusting agent, and, for example, the number average particle diameter of the above-described colorant is 0.01 to 1.5 μm. The content of the colorant in the overcoat coating film is, for example, 2 to 20 vol %.

The above-described overcoat coating film may further contain an extender pigment. Examples of the extender pigment include barium sulfate, titanium oxide and the like. The above-described extender pigment is sufficiently smaller relative to the above-described gloss adjusting agent, and, for example, the number average particle diameter of the above-described extender pigment is 0.01 to 1 μm. The content of the extender pigment in the overcoat coating film is, for example, 0.1 to 15 vol %.

The above-described overcoat coating film may further contain a lubricant, from the viewpoint of preventing the occurrence of galling in the overcoat coating film on processing the coated metal sheet. Example of the lubricant include organic waxes such as fluorine-based wax, polyethylene-based wax, styrene-based wax, polypropylene-based wax and the like, and inorganic lubricants such as molybdenum disulfide, talc and the like. The content of the lubricant in the overcoat coating film is, for example, 0 to 10 vol %.

The above-described overcoat coating film is produced by a known method that includes applying a coating material for overcoat coating films to the surface of the above-described metal sheet, the surface of the undercoat coating film described below or the like, drying the coating material, and curing the coating material as required. The coating material for overcoat coating films contains materials for the overcoat coating film aforementioned, and may further contain other ingredients besides the materials in the range where the effect of the present embodiment can be achieved.

For example, the coating material for overcoat coating films may further contain a curing agent. The above-described curing agent crosslinks the polyester or acrylic resin aforementioned on curing (baking) when the overcoat coating film is produced. The type of the curing agent can be selected from the crosslinking agent aforementioned and known curing agents as appropriate, depending on the type of the resin to be used, baking conditions and the like.

Examples of the above-described curing agent include melamine compounds, isocyanate compounds, combinations of a melamine compound and an isocyanate compound and the like. Examples of the melamine compound include imino group-type, methylol-imino group-type, methylol group-type, or complete alkyl group-type melamine compounds. The isocyanate compound may be any of aromatic, aliphatic, and alicyclic compounds, and examples include m-xylene diisocyanate, hexamethylene diisocyanate, naphthalene diisocyanate, isophorone diisocyanate, and block compounds of these.

The overcoat coating film may further contain a curing catalyst as appropriate in the range where the storage stability of the coating material for overcoat coating films is not affected. The content of the above-described curing agent in the overcoat coating film is for example, 10 to 30 vol %.

The overcoat coating film may also contain 10 vol % or less of an ultraviolet absorber (UVA) and a light stabilizer (HALS) as appropriate in order to further improve the weather resistance. Furthermore, the overcoat coating film may contain a hydrophilizing agent, for example, 30 vol % or less of a partially hydrolyzed condensate of tetraalkoxysilane for prevention of rain streak stains.

The above-described coated metal sheet may have further components, in the range where the effect of the present embodiment can be exerted. For example, the above-described coated metal sheet preferably further may have an undercoat coating film between the above-described metal sheet and the overcoat coating film, from the viewpoint of improving the adhesiveness and the corrosion resistance of the overcoat coating film in the coated metal sheet. The above-described undercoat coating film is disposed on the surface of the metal sheet, or, when the above-described chemical conversion film has been made, on the surface of the chemical conversion film.

The above-described undercoat coating film is composed of resin. Examples of the resin include epoxy resin, polyester, epoxy-modified polyester resin, acrylic resin, and phenoxy resin.

The above-described undercoat coating film may further contain an anti-rust pigment, a coloring pigment, a metallic pigment, an extender pigment or the like. Examples of the above-described anti-rust pigment include non-chromium-based anti-rust pigments such as modified silica, vanadates, magnesium hydrogenphosphate, magnesium phosphate, zinc phosphate, aluminum polyphosphate and the like, and chromium-based anti-rust pigments such as strontium chromate, zinc chromate, barium chromate, calcium chromate and the like. Example of the above-described coloring pigment include titanium oxide, carbon black, chromium oxide, iron oxide, colcothar, titanium yellow, cobalt blue, cobalt green, Aniline Black, and Phthalocyanine Blue. Example of the above-described metallic pigment include aluminum flakes (non-leafing type), bronze flakes, copper flakes, stainless steel flakes, and nickel flakes. Examples of the above-described extender pigment include barium sulfate, titanium oxide, silica, and calcium carbonate.

The content of the above-described pigment in the undercoat coating film can be determined as appropriate, in the range where the effect of the present embodiment can be achieved. For example, the content of the above-described anti-rust pigment in the above-described undercoat coating film is preferably, for example, 10 to 70 vol %.

Also, the above-described coated metal sheet further has an intercoat coating film between the above-described undercoat coating film and the above-described overcoat coating film, from the viewpoint of improving the adhesiveness and the corrosion resistance of the overcoat coating film in the coated metal sheet.

The above-described intercoat coating film is composed of resin. Examples of the resin include fluorine resin such as polyvinylidene fluoride and the like, polyester, polyester-modified silicones, acrylic resin, polyurethane, and polyvinyl chloride. The above-described intercoat coating film also may further contain additives such as an anti-rust pigment, a coloring pigment, a metallic pigment, or the like, similarly as the above-described undercoat coating film, in the range where the effect of the present embodiment can be achieved.

The coated metal sheet according to the present embodiment is a chromate-free or chromate-based coated metal sheet. “Chromate-free” means that the above-described coated metal sheet contains substantially no hexavalent chromium. It is possible to confirm that the above-described coated metal sheet is “chromate-free” as follows. For example, in any of the metal sheet, the chemical conversion film, the undercoat coating film, and the overcoat coating film aforementioned, four 50 mm×50 mm specimens are cut off from a metal sheet on which the overcoat coating film or the undercoat coating film has been produced singly, and the specimens are immersed in 100 mL of boiling pure water for 10 minutes. Then, when hexavalent chromium eluted in pure water is quantified by a concentration analysis method in compliance with JIS H8625, Annex 2. 4. 1, “Diphenylcarbazide Visual Colorimetric Method”, the concentration shall be lower than the detection limit. Hexavalent chromium is not eluted form the above-described coated metal sheet during actual use into the environment, and the above-described coated metal sheet exhibits sufficient corrosion resistance at its flat portion. Incidentally, a “flat portion” refers to a portion that is covered with the above-described overcoat coating film of the above-described metal sheet and has not been deformed by bending, drawing, bulging, embossing, roll-forming or the like.

The above-described coated metal sheet is suitable for a matte-coated metal sheet. Matte refers to a glossiness at 75° being from 1 to 25. When the glossiness is extremely high, an enamel-like gloss may predominate, and a matte feeling may not be achieved. The above-described glossiness is adjusted with the average particle diameter of the gloss adjusting agent and matting agent, their contents in the overcoat coating film and the like.

The method for producing the above-described coated metal sheet include a first step of applying an overcoat coating material that contains the above-described resin, the above-described gloss adjusting agent, and the above-described matting agent onto the above-described metal sheet and a second step of curing the coating film of the overcoat coating material to form the above-described overcoat coating film.

In the above-described first step, the above-described overcoat coating material may be applied directly onto the surface of the above-described metal sheet, may be applied onto the above-described chemical conversion film formed on the surface of the above-described metal sheet, or may be applied onto the above-described undercoat coating film formed on the surface of the coated metal sheet or the surface of the chemical conversion film.

The above-described overcoat coating material is prepared by, for example, dispersing the materials for the overcoat coating film aforementioned in a solvent. The coating material may contain a solvent, a crosslinking agent and the like. Examples of the above-described solvent include hydrocarbons such as toluene, xylene and the like; esters such as ethyl acetate, butyl acetate and the like; ethers such as cellosolve and the like; and ketones such as methyl isobutyl ketone, methyl ethyl ketone, isophorone, cyclohexanone and the like.

The above-described overcoat coating material is applied, for example, by a known method such as roll coating, curtain flow coating, spray coating, immersion coating and the like. The amount of the above-described overcoat coating material coated is adjusted as appropriate, depending on the intended film thickness T of the overcoat coating film.

Incidentally, as aforementioned, blending a matting agent into the overcoat coating film allows a unique design to be exhibited as well as can improve the scratch resistance of the coated metal sheet. In order to achieve both the designability and the scratch resistance, the overcoat coating film is preferably coated thicker than a coating film that contains a gloss adjusting agent only and contains no matting agent. Also, since the ratio of nonvolatile ingredients in the coating material increases by blending a matting agent into the overcoat coating film, the overcoat coating film can be coated thicker than a coating film that contains a gloss adjusting agent only and contains no matting agent.

The above-described gloss adjusting agent contained in the above-described overcoat coating material satisfies the aforementioned size conditions. In the above-described overcoat coating material, when the above-described gloss adjusting agent does not satisfy the aforementioned size conditions, the above-described overcoat coating material that satisfies the above-described conditions can be obtained by subjecting the above-described overcoat coating material to treatment for pulverizing the particles in the overcoat coating material. Examples of the above-described “treatment for pulverizing the particles” include roller mill treatment. More specifically, the treatment is conducted by appropriately setting the clearance between the rollers of the roller mill and treatment time such that the above-described Ru falls below 1.2T before a matting agent is blended to the overcoat coating material. Thereafter, the above-described overcoat coating material that satisfies the above-described conditions can be obtained by blending the matting agent.

The above-described second step can be conducted, for example, by a known method for baking the above-described overcoat coating material onto a metal sheet. For example, in the second step, a metal sheet to which a coating material for overcoat coating films has been applied is heated such that the temperature of the metal sheet reaches 200 to 250° C.

The production method of the above-described coated metal sheet may include other steps other than the first step and second step aforementioned, in the range where the effect of the present invention can be achieved. Examples of the other steps include a step for forming a chemical conversion film, a step for forming an undercoat coating film, and a step for forming an intercoat coating film.

The above-described chemical conversion film can be formed by applying an aqueous chemical conversion liquid for forming the film by a known method such as roll-coating, spin-coating, spraying methods and the like, to the above-described metal sheet surface and drying the above-described metal sheet after application without water washing. The drying temperature and the drying time for the metal sheet are preferably 60 to 150° C. as the temperature which the metal sheet reaches and 2 to 10 seconds, for example, from the viewpoint of productivity.

The above-described undercoat coating film is produced by application of a coating material for undercoat coating films. The coating material may contain a solvent, a crosslinking agent and the like. Examples of the above-described solvent include hydrocarbons such as toluene xylene and the like; esters such as ethyl acetate, butyl acetate and the like; ethers such as cellosolve and the like; and ketones such as methyl isobutyl ketone, methyl ethyl ketone, isophorone, cyclohexanone and the like. Examples of the above-described crosslinking agent include melamine resin, isocyanate resin and the like for crosslinking the resin aforementioned. The coating material for undercoat coating films is prepared by homogeneously mixing and dispersing the materials aforementioned.

The coating material for undercoat coating films is applied by a known method such as roll coating, curtain flow coating, spray coating, immersion coating or the like to a metal sheet in an amount to be coated such that a dry film thickness of 1 to 10 μm, preferably 3 to 7 μm is obtained. A coating film of the coating material is produced by heating a metal sheet at, for example, 180 to 240° C., a temperature which the metal sheet achieves, thereby baking the film onto the metal sheet.

The above-described intercoat coating film is also produced by application of a coating material for intercoat coating films, similarly as the undercoat coating film. The coating material may contain the above-described solvent, the above-described crosslinking agent and the like in addition to the materials for the intercoat coating film. The coating material for intercoat coating films is prepared by homogeneously mixing and dispersing the materials aforementioned. The coating material for intercoat coating films is preferably applied, for example, by the above-described known method, to the undercoat coating film in an amount to be coated such that the sum of the dry film thickness of the coating material and the film thickness of the undercoat coating film reaches 1 to 10 μm (preferably 3 to 7 μm), from the viewpoint of the processability. A coating film of the coating material is produced by heating a metal sheet at, for example, 180 to 240° C., a temperature which the metal sheet achieves, thereby baking the film onto the metal sheet.

Applications of the above-described coated metal sheet are suitable for exterior use. “For exterior use” refers to being used in portions exposed to the open air such as roofs, walls, accessories, signboards, outdoor-installed apparatuses and the like, wherein the portions may be irradiated with a sunbeam and its reflected light. Examples of the coated metal sheet for exterior use include coated metal sheets for exterior building materials and the like.

The above-described coated metal sheet is formed into an exterior building material by known processing such as bending, drawing, bulging, embossing, roll-forming or the like. In this manner, the exterior building material is composed of the above-described coated metal sheet. The exterior building material may further include other structure in the range where the above-described effects can be achieved. For example, the above-described exterior building material may further have a structure to be subjected to appropriate installation during actual use of the exterior building material. Examples of such a structure include members to fix an exterior building material to a building, members to connect a plurality of exterior building materials, marks that show the direction of an exterior building material on mounting, foam sheets and foam layers to improve the thermal insulation properties and the like. These structures may be included in the coated metal sheet for exterior use aforementioned.

In the above-described coated metal sheet, the above-described gloss adjusting agent (microporous particles) is sufficiently confined in the overcoat coating film. Additionally, the particle diameter of the gloss adjusting agent in the above-described overcoat coating film in the film thickness direction of the overcoat coating film is likely to become sufficiently small as its particle shape is lower-profile. Furthermore, about 97.5% by number, that is, the most portion of the above-described gloss adjusting agent has a sufficiently small particle diameter of 0.7T or less relative to the film thickness T of the overcoat coating film. Thus, the above-described overcoat coating film can be designed such that the above-described microporous particles are not exposed within the intended age of service, even if the resin in the overcoat coating film is gradually worn from the surface of the overcoat coating film by actual use in an exterior application.

Meanwhile, in the above-described coated metal sheet, although the matting agent is covered with the resin constituting the overcoat coating film, at least a part of the particles in the matting agent is larger than the film thickness of a portion of the overcoat coating film where the matting agent is not contained. Thus, the matting agent may appear from the overcoat coating film when the resin in the overcoat coating film is gradually worn from the surface of the overcoat coating film by actual use in an exterior application, even during the intended age of service. In such a situation, if microporous particles as the matting agent are blended in the overcoat coating film, a portion of the overcoat coating film where the matting agent cracks, collapses, or falls off may become an origin of corrosion. Thus, primary particles are blended as the matting agent in the above-described coated metal sheet. Therefore, even if the above-described primary particles appear from the surface of the overcoat coating film by actual use in an exterior application, cracking and collapse as those occurring in microporous particles and fall-off from the above-described overcoat coating film are prevented, and corrosive factors such as rainwater cannot reach the metal sheet.

Therefore, cracking, collapse, and falling-off from the above-described overcoat coating film of the above-described gloss adjusting agent (microporous particles) and cracking, collapse, and falling-off from the overcoat coating film of the above-described matting agent (primary particles) within the intended age of service are prevented, and corrosive factors such as rainwater and the like cannot reach the metal sheet during the intended age of service. Thus, the above-described coated metal sheet, if being chromate-free (if the above-described metal sheet has been non-chromate anti-rust treated), exhibits flat portion-corrosion resistance at least equivalent to that of conventional chromate-treated coated metal sheets, and if having been subjected to chromate treatment, exhibits flat portion-corrosion resistance equivalent to or greater than that of conventional chromate-treated coated metal sheets. Examples of the “chromate treatment” of the coated metal sheet in the embodiment include, in addition to the chromate anti-rust treatment of the above-described metal sheet, the adoption of an undercoat coating film containing a chromate-based anti-rust pigment. Examples of the “coated metal sheet subjected to chromate treatment” include coated metal sheets that have a non-chromate anti-rust treated metal sheet and an undercoat coating film containing a chromate-based anti-rust pigment, coated metal sheets that has a chromate anti-rust treated metal sheet and an undercoat coating film containing no chromate-based anti-rust pigment, and coated metal sheet that have a chromate anti-rust treated metal sheet and an undercoat coating film containing a chromate-based anti-rust pigment.

As clear from the above description, according to the present embodiment, there can be provided a coated metal sheet which, even being chromate-free, has sufficient flat-portion corrosion resistance, wherein the coated metal sheet has a metal sheet and an overcoat coating film to be disposed on/above the metal sheet, wherein the overcoat coating film contains a gloss adjusting agent which is particles having micropores (microporous particles) and a matting agent which is primary particles, wherein the content of the above-described gloss adjusting agent in the above-described overcoat coating film is from 0.2 to 15 vol %, and the content of the above-described matting agent in the above-described overcoat coating film is from 0.2 to 15 vol %, and wherein the following equations are satisfied:

D1_(97.5) /T≦0.7

Ru≦1.2T

R1≧2.0

2.0≦D2_(97.5) /T≦7.0

13≦T≦20

wherein R1 (μm) is the number average particle diameter of the gloss adjusting agent, T (μm) is the film thickness of the above-described overcoat coating film, D1_(97.5) (μm) is the 97.5% particle diameter in the number particle size distribution of the above-described gloss adjusting agent, D2_(97.5) (μm) is the 97.5% particle diameter in the accumulated particle size distribution of the above-described matting agent based on the number of particles, and Ru (μm) is the upper limit particle diameter in the number particle size distribution of the above-described gloss adjusting agent.

Additionally, according to the present embodiment, there can be provided a coated metal sheet which, even being chromate-free, has sufficient flat-portion corrosion resistance, wherein the coated metal sheet has a metal sheet, an intercoat coating film to be disposed on/above the metal sheet, and an overcoat coating film to be disposed on the intercoat coating film, wherein the overcoat coating film contains a gloss adjusting agent which is particles having micropores (microporous particles) and a matting agent which is primary particles, wherein the content of the above-described gloss adjusting agent in the above-described overcoat coating film is from 0.01 to 15 vol %, and the content of the matting agent in the overcoat coating film is from 0.01 to 15 vol %, and wherein the following equations are satisfied:

D1_(97.5) /T≦0.7

Ru≦1.2T

R1≧1.0

0.5≦D2_(97.5) /T≦7.0

3≦T≦20

wherein R1 (μm) is the number average particle diameter of the gloss adjusting agent, T (μm) is the film thickness of the above-described overcoat coating film, D1_(97.5) (μm) is the 97.5% particle diameter in the number particle size distribution of the above-described gloss adjusting agent, D2_(97.5) (μm) is the 97.5% particle diameter in the accumulated particle size distribution of the above-described matting agent based on the number of particles, and Ru (μm) is the upper limit particle diameter in the number particle size distribution of the above-described gloss adjusting agent.

The fact that the above-described Ru is less than T is even more effective, from the viewpoint of further improvement of the flat portion-corrosion resistance of the coated metal sheet, or from the viewpoint of further prolongation of the life of the coated metal sheet having sufficient flat portion-corrosion resistance.

Additionally, the fact that the above-described metal sheet has been subjected to non-chromate anti-rust treatment and the above-described coated metal sheet is chromate-free is even more effective, from the viewpoint of reducing environmental loads in use or production of the coated metal sheet, and the fact that the above-described metal sheet has been subjected to chromate anti-rust treatment is even more effective, from the viewpoint of further improvement of the flat portion-corrosion resistance of the coated metal sheet.

Also, the fact that the above-described gloss adjusting agent is silica particles is even more effective, from the viewpoint of inexpensively producing coated metal sheets having the intended designability.

Also, the fact that the above-described coated metal sheet further has an undercoat coating film between the above-described metal sheet and the above-described overcoat coating film is more effective from the viewpoint of improving the adhesiveness and corrosion resistance of the overcoat coating film in the coated metal sheet, and the fact that the above-described coated metal sheet further has an undercoat coating film between the above-described metal sheet and the above-described intercoat coating film is even more effective, from the above-described viewpoint.

Also, when the above-described coated metal sheet has a glossiness at 75° of 1 to 25, both the intended designability and sufficient flat portion-corrosion resistance are achieved.

Additionally, the fact that the above-described coated metal sheet is a coated metal sheet for exterior use is further effective from the viewpoint of reducing a load on the environment due to elution of chromium during actual use.

An exterior building material composed of the above-described coated metal sheet is chromate-free as well as can exhibit excellent flat portion-corrosion resistance during actual use of 10 years or more.

Additionally, the aforementioned method for producing a coated metal sheet having the above-described metal sheet and the overcoat coating film to be disposed on the above-described metal sheet comprises the steps of: applying an overcoat coating material that contains a resin, a gloss adjusting agent, and a matting agent onto the above-described metal sheet and curing the coating film of the above-described overcoat coating material to form the above-described overcoat coating film, wherein the content of the above-described gloss adjusting agent in the overcoat coating film is from 0.2 to 15 vol %, and the content of the matting agent in the above-described overcoat coating film is from 0.2 to 15 vol %, wherein the above-described gloss adjusting agent is particles having micropores, and the matting agent is primary particles, and wherein the gloss adjusting agent and the matting agent which satisfy the following equations are employed:

D1_(97.5) /T≦0.7

Ru≦1.2T

R1≧2.0

2.0≦D2_(97.5) /T≦7.0

13≦T≦20

wherein R1 (μm) is the number average particle diameter of the gloss adjusting agent, T (μm) is the film thickness of the above-described overcoat coating film, D1_(97.5) (μm) is the 97.5% particle diameter in the number particle size distribution of the above-described gloss adjusting agent, D2_(97.5) (μm) is the 97.5% particle diameter in the accumulated particle size distribution of the above-described matting agent based on the number of particles, and Ru (μm) is the upper limit particle diameter in the number particle size distribution of the above-described gloss adjusting agent. Accordingly, it is possible to provide a coated metal sheet which, although being chromate-free, has excellent flat-portion corrosion resistance equivalent to or greater than that of coated metal sheets comprising a chromate anti-rust treated metal sheet.

Additionally, the aforementioned method for producing a coated metal sheet having the above-described metal sheet, an intercoat coating film to be disposed on the above-described metal sheet, and an overcoat coating film to be disposed on the intercoat coating film comprises the steps of: applying an overcoat coating material that contains a resin, a gloss adjusting agent, and a matting agent onto the above-described metal sheet and curing the coating film of the above-described overcoat coating material to form the above-described overcoat coating film, wherein the content of the gloss adjusting agent in the overcoat coating film is from 0.01 to 15 vol %, and the content of the above-described matting agent in the above-described overcoat coating film is from 0.01 to 15 vol %, wherein the above-described gloss adjusting agent is particles having micropores, and the matting agent is primary particles, and wherein the above-described gloss adjusting agent and matting agent which satisfy the following equations are employed:

D1_(97.5) /T≦0.7

Ru≦1.2T

R1≧1.0

0.5≦D2_(97.5) /T≦7.0

3≦T≦20

wherein R1 (μm) is the number average particle diameter of the gloss adjusting agent, T (μm) is the film thickness of the above-described overcoat coating film, D1_(97.5) (μm) is the 97.5% particle diameter in the number particle size distribution of the above-described gloss adjusting agent, D2_(97.5) (μm) is the 97.5% particle diameter in the accumulated particle size distribution of the matting agent based on the number of particles, and Ru (μm) is the upper limit particle diameter in the number particle size distribution of the above-described gloss adjusting agent. Accordingly, it is possible to provide a coated metal sheet which, although being chromate-free, has excellent flat-portion corrosion resistance equivalent to or greater than that of coated metal sheets comprising a chromate anti-rust treated coated metal sheet.

In the above-described production method, when the above-described overcoat coating material has been subjected to treatment for pulverizing the particles in the above-described overcoat coating material, coarse particles present accidentally and irregularly in the overcoat coating film are substantially removed from the overcoat coating material. Thus, the treatment is even more effective, from the viewpoint of further improvement of the flat portion-corrosion resistance of the coated metal sheet.

Hereinafter, the present invention will be described in more detail with reference to Examples, but the present invention is not limited by these Examples.

EXAMPLES

[Production of Coated Base Sheets 1 to 5]

A hot-dip 55% Al—Zn alloy-plated steel sheet having an amount deposited on both the sides of 150 g/m² was alkali-degreased (base sheet 1). Subsequently, a non-chromate anti-rust treatment solution described below at 20° C. was applied to the surface of the plated layer of the plated steel sheet, as pre-coating treatment. The plated steel sheet was dried at 100° C. without washing with water to thereby obtain a non-chromate anti-rust treated plated steel sheet having an amount of deposited of 10 mg/m² in terms of Ti (base sheet 2).

(Non-Chromate Anti-Rust Treatment Solution)

Hexafluorotitanate 55 g/L Hexafluorozirconate 10 g/L Aminomethyl-substituted polyvinyl phenol 72 g/L Water Balance

Additionally, to a surface of base sheet 2, the following undercoat coating material based on epoxy resin was applied. The above-described chemical conversion steel sheet was heated such that the temperature of the above-described plated steel sheet reached 200° C. to thereby obtain the above-described chromate-free plated steel sheet including an undercoat coating film having a dry film thickness of 5 μm (base sheet 3).

Phosphate mixture 15 vol %  Barium sulfate 5 vol % Silica 1 vol % Clear coating material Balance

Alternatively “SURFCOAT NRC300NS” manufactured by Nippon Paint Co., Ltd. (“SURFCOAT” is a registered trademark of the company), which is a chromate treatment solution, was used instead of the above-described chromate-free treatment solution to conduct chromate anti-rust treatment of an amount deposited of 20 mg/m² in terms of chromium. Subsequently, to the surface of the above-described chromate anti-rust treated plated steel sheet, the following undercoat coating material based on epoxy resin was applied. The above-described chemical conversion steel sheet was heated such that the temperature of the above-described plated steel sheet reached 200° C. to thereby obtain a plated steel sheet including a chromate-based undercoat coating film having a dry film thickness of 5 μm (base sheet 4).

Strontium chromate 15 vol %  Barium sulfate 5 vol % Silica 1 vol % Clear coating material Balance

Incidentally, in the above-described undercoat coating material, the above-described clear coating material is “NSC680” manufactured by Nippon Fine Coatings Co., Ltd. In the above-described undercoat coating material, the above-described phosphate mixture is a mixture of magnesium hydrogenphosphate, magnesium phosphate, zinc phosphate, and aluminum tripolyphosphate. Also, the above-described silica is a extender pigment and has an average particle diameter of 5 μm. Additionally, the above-described vol % is a proportion based on the solid content in the undercoat coating material.

Alternatively, to a surface of base sheet 3, the following intercoat coating material based on polyester was applied. The above-described chemical conversion steel sheet was heated such that the temperature of the above-described plated steel sheet reached 220° C. to thereby obtain the above-described chromate-free plated steel sheet including an intercoat coating film having a dry film thickness of 5 μm on the above-described undercoat coating film (base sheet 5).

Carbon black 7 vol % Silica particles 1 1 vol % Polyester-based coating material Balance

The above-described polyester-based coating material is “CA clear coating material” manufactured by Nippon Fine Coatings Co., Ltd., which is a polyester-based coating material (PE). Carbon black is a coloring pigment. The vol % described above is a proportion based on the solid content in the overcoat coating material.

Also, silica particles 1 described above (silica 1) are a classified material or its mixture, for example, and have a particle size distribution like the normal distribution. The number average particle diameter R1 of the silica particles 1 is 3.0 μm, and D1_(97.5) in the number particle size distribution is 6.1 μm. Additionally, the upper limit particle diameter Ru in the number particle size distribution is 12.0 μm.

The following ingredients were mixed in the following amounts to thereby obtain an overcoat coating material.

Carbon black 7 vol % Silica particles 1 5 vol % Acrylic particles 1 5 vol % Clear coating material 1 Balance

The above-described clear coating material 1 described above is “CA clear coating material” manufactured by Nippon Fine Coatings Co., Ltd., which is a polyester-based coating material (PE). Carbon black is a coloring pigment. The vol % described below is a proportion based on the solid content in the overcoat coating material.

Acrylic particles 1 described above (acrylic 1) have a particle size distribution like the normal distribution. Acrylic particles 1, which have been produced by suspension polymerization, correspond to the aforementioned primary particles. The number average particle diameter R2 of acrylic particles 1 is 35 μm, and D2_(97.5) in the number particle size distribution is 50 μm.

[Production of Coated Metal Sheet 1]

The above-described overcoat coating material was applied to the surface of the undercoat coating film of base sheet 3. Base sheet 3 was heated such that the temperature of the above-described plated steel sheet in base sheet 3 reached 220° C. to thereby produce an overcoat coating film having a dry film thickness T of 15 μm. Coated metal sheet 1 was thus produced.

Incidentally, coated metal sheet 1 was cut to allow its cross section to be exposed. The above-described cross section was encapsulated inside a mass of epoxy resin, further ground, and photographed with a scanning electron microscope. The resulting images of a plurality of spots were processed and analyzed to determine the particle size distribution of silica particles 1 and acrylic particles 1. R1, R2, D1_(97.5), D2_(97.5), and Ru were confirmed to be substantially equivalent to the above-described numerical values.

[Production of Coated Metal Sheets 2 to 4]

Coated metal sheet 2 was produced in the same manner as coated metal sheet 1 except that the amount of the overcoat coating material deposited was changed such that the dry film thickness T reached 13 μm. Additionally, coated metal sheet 3 was produced in the same manner as coated metal sheet 1 except that the amount of the overcoat coating material deposited was changed such that the dry film thickness T reached 10 μm. Furthermore, coated metal sheet 4 was produced in the same manner as coated metal sheet 1 except that the amount of the overcoat coating material deposited was changed such that the dry film thickness T reached 22 μm.

[Production of Coated Metal Sheets 5 to 8]

Coated metal sheet 5 was produced in the same manner as coated metal sheet 1 except that silica particles 2 were used instead of silica particles 1 as the gloss adjusting agent in the overcoat coating material. Silica particles 2 are a classified material or its mixture, wherein R1 is 8.2 μm, D1_(97.5) is 10.4 μm, and Ru is 18.8 μm.

Additionally, coated metal sheet 6 was produced in the same manner as coated metal sheet 2 except that silica particles 3 were used instead of silica particles 1 as the gloss adjusting agent in the overcoat coating material. Silica particles 3 are a classified material or its mixture, wherein R1 is 5.5 μm, D1_(97.5) is 9.6 μm, and Ru is 10.8 μm.

Additionally, coated metal sheet 7 was produced in the same manner as coated metal sheet 1 except that silica particles 4 were used instead of silica particles 1 as the gloss adjusting agent in the overcoat coating material. Silica particles 4 are a classified material or its mixture, for example, wherein R1 is 3.7 μm, D1_(97.5) is 5.4 μm, and Ru is 7.0 μm.

Additionally, coated metal sheet 8 was produced in the same manner as coated metal sheet 1 except that silica particles 5 were used instead of silica particles 1 as the gloss adjusting agent in the overcoat coating material. Silica particles 5 are a classified material or its mixture, for example, wherein R1 is 0.7 μm, D1_(97.5) is 1.4 μm, and Ru is 2.0 μm.

[Production of Coated Metal Sheets 9 to 11]

Coated metal sheet 9 was produced in the same manner as coated metal sheet 1 except that the content of the silica particles in the overcoat coating material was changed to 0.1 vol %. Additionally, coated metal sheet 10 was produced in the same manner as coated metal sheet 1 except that the content of the silica particles in the overcoat coating material was changed to 13 vol %. Additionally, coated metal sheet 11 was produced in the same manner as coated metal sheet 1 except that the content of the silica particles in the overcoat coating material was changed to 20 vol %.

[Production of Coated Metal Sheet 12]

Coated metal sheet 12 was produced in the same manner as coated metal sheet 1 except that acrylic particles 2 were used instead of acrylic particles 1 as the matting agent in the overcoat coating material. Acrylic particles 2, which have been produced by suspension polymerization, correspond to the aforementioned primary particles. In acrylic particles 2, R2 is 10.0 μm, and D2_(97.5) is 15.0 μm.

[Production of Coated Metal Sheet 13]

Coated metal sheet 13 was produced in the same manner as coated metal sheet 1 except that acrylic particles 3 were used instead of acrylic particles 1 as the matting agent in the overcoat coating material. Acrylic particles 3, which have been produced by suspension polymerization, correspond to the aforementioned primary particles. In acrylic particles 3, R2 is 80.0 μm, and D2_(97.5) is 120.0 μm.

[Production of Coated Metal Sheet 14]

Coated metal sheet 14 was produced in the same manner as coated metal sheet 1 except that polyacrylonitrile (PAN) particles 1 were used instead of acrylic particles 1 as the matting agent in the overcoat coating material. PAN particles 1, which have been produced by a spray dry method, correspond to the aforementioned microporous particles. In PAN particles 1, R2 is 10.7 μm, D2_(97.5) is 33.0 μm.

[Production of Coated Metal Sheet 15]

Coated metal sheet 15 was produced in the same manner as coated metal sheet 1 except that acrylic particles 4 were used instead of acrylic particles 1 as the matting agent in the overcoat coating material. In acrylic particles 4, R2 is 60.0 μm, and D2_(97.5) is 70.0 μm.

[Production of Coated Metal Sheets 16 to 18]

Coated metal sheet 16 was produced in the same manner as coated metal sheet 1 except that the content of the acrylic particles in the overcoat coating material was changed to 0.1 vol %. Additionally, coated metal sheet 17 was produced in the same manner as coated metal sheet 1 except that the content of the acrylic particles in the overcoat coating material was changed to 13 vol %. Additionally, coated metal sheet 18 was produced in the same manner as coated metal sheet 1 except that the content of the acrylic particles in the overcoat coating material was changed to 20 vol %.

[Production of Coated Metal Sheets 19 and 20]

Coated metal sheet 19 was produced in the same manner as coated metal sheet 12 except that the overcoat coating film was formed on base sheet 5 instead of on base sheet 3, silica particles 17 were used instead of silica particles 1 as the gloss adjusting agent in the overcoat coating film, and the amount of the overcoat coating material deposited was changed such that the dry film thickness T reached 2.2 μm. Silica particles 17 are a classified material or its mixture, for example, wherein R1 is 1.0 μm, D1_(97.5) is 1.4 μm, and Ru is 1.5 μm.

Coated metal sheet 20 was produced in the same manner as coated metal sheet 19 except that silica particles 18 were used instead of silica particles 1 as the gloss adjusting agent in the overcoat coating film, and the amount of the overcoat coating material deposited was changed such that the dry film thickness T reached 3 μm. Silica particles 18 are a classified material or its mixture, for example, wherein R1 is 1.0 μm, D1_(97.5) is 2.0 μm, and Ru is 2.6 μm.

[Production of Coated Metal Sheet 21]

Coated metal sheet 21 was produced in the same manner as coated metal sheet 1 except that the amount of the overcoat coating material deposited was changed such that the dry film thickness T reached 20 μm.

[Production of Coated Metal Sheets 22 to 25]

Coated metal sheet 22 was produced in the same manner as coated metal sheet 1 except that the overcoat coating film was formed on base sheet 5 instead of on base sheet 3, and the content of the silica particles in the overcoat coating material was changed to 0.01 vol %. Additionally, coated metal sheet 23 was produced in the same manner as coated metal sheet 22 except that the content of the silica particles in the overcoat coating material was changed to 0.0005 vol %. Additionally, coated metal sheet 24 was produced in the same manner as coated metal sheet 22 except that the content of the silica particles in the overcoat coating material was changed to 15 vol %. Furthermore, coated metal sheet 25 was produced in the same manner as coated metal sheet 22 except that the content of the silica particles in the overcoat coating material was changed to 16 vol %.

[Production of Coated Metal Sheet 26]

Coated metal sheet 26 was produced in the same manner as coated metal sheet 1 except that the overcoat coating film was formed on base sheet 5 instead of on base sheet 3, and acrylic particles 5 were used instead of acrylic particles 1 as the matting agent in the overcoat coating film. Acrylic particles 5 are a classified material or its mixture, for example, wherein R2 is 5.0 μm, and D2_(97.5) is 7.2 μm.

[Production of Coated Metal Sheets 27 to 30]

Coated metal sheet 27 was produced in the same manner as coated metal sheet 1 except that the overcoat coating film was formed on base sheet 5 instead of on base sheet 3, and the content of the acrylic particles in the overcoat coating material was changed to 0.01 vol %. Additionally, coated metal sheet 28 was produced in the same manner as coated metal sheet 27 except that the content of the acrylic particles in the overcoat coating material was changed to 0.0005 vol %. Additionally, coated metal sheet 29 was produced in the same manner as coated metal sheet 27 except that the content of the acrylic particles in the overcoat coating material was changed to 15 vol %. Furthermore, coated metal sheet 30 was produced in the same manner as coated metal sheet 27 except that the content of the acrylic particles in the overcoat coating material was changed to 16 vol %.

[Production of Coated Metal Sheets 31 to 33]

Coated metal sheet 31 was produced in the same manner as coated metal sheet 1 except that the overcoat coating film was formed on base sheet 1 instead of on base sheet 3. Additionally, coated metal sheet 32 was produced in the same manner as coated metal sheet 1 except that the overcoat coating film was formed on base sheet 2 instead of on base sheet 3. Additionally, coated metal sheet 33 was produced in the same manner as coated metal sheet 1 except that the overcoat coating film was formed on base sheet 4 instead of on base sheet 3.

[Production of Coated Metal Sheets 34 and 35]

Coated metal sheet 34 was obtained in the same manner as coated metal sheet 1 except that clear coating material 2 was used instead of clear coating material 1 of the overcoat coating material. Clear coating material 2 is “QK clear coating material” manufactured by Nippon Fine Coatings Co., Ltd., which is a polyester-based coating material (PE). Additionally, coated metal sheet 35 was obtained in the same manner as coated metal sheet 1 except that clear coating material 3 was used instead of clear coating material 1. Clear coating material 3 is “NSC3300 clear coating material” manufactured by Nippon Fine Coatings Co., Ltd., which is a polyester-based coating material (PE).

[Production of Coated Metal Sheets 36 and 37]

Coated metal sheet 36 was produced in the same manner as coated metal sheet 1 except that polyacrylonitrile (PAN) particles 2 were used instead of silica particles 1 of the overcoat coating material. PAN particles 2 are a classified material or its mixture, for example, wherein R1 is 5.0 μm, D1_(97.5) is 7.6 μm, and Ru is 9.5 μm. Additionally, coated metal sheet 37 was produced in the same manner as coated metal sheet 1 except that calcium carbonate-calcium phosphate composite (CaCPC) particles were used instead of silica particles 1 of the overcoat coating material. The CaCPC particles are a classified material or its mixture, wherein R1 is 5.0 μm, D1_(97.5) is 7.6 μm, and Ru is 9.5 μm.

[Production of Coated Metal Sheets 38 and 39]

Additionally, coated metal sheet 38 was produced in the same manner as coated metal sheet 1 except that silica particles 6 were used instead of silica particles 1 as the gloss adjusting agent in the overcoat coating material. Silica particles 6 are a classified material or its mixture, for example, wherein R1 is 5.0 μm, D1_(97.5) is 7.6 μm, and Ru is 14.0 μm.

Additionally, coated metal sheet 39 was produced in the same manner as coated metal sheet 1 except that silica particles 7 were used instead of silica particles 1 as the gloss adjusting agent in the overcoat coating material. Silica particles 7 are a classified material or its mixture, for example, wherein R1 is 7.5 μm, D1_(97.5) is 9.2 μm, and Ru is 14.8 μm.

[Production of Coated Metal Sheet 40]

Coated metal sheet 40 was obtained in the same manner as coated metal sheet 1 except that glass particles were used instead of acrylic particles 1 of the overcoat coating material. The glass particles correspond to the aforementioned primary particles. In the glass particles, R2 is 20.0 μm, and D2_(97.5) is 30.0 μm.

[Production of Coated Metal Sheets 41 to 43]

Coated metal sheet 41 was produced in the same manner as coated metal sheet 38 except that the overcoat coating film was formed on base sheet 4 instead of on base sheet 3. Additionally, coated metal sheet 42 was produced in the same manner as coated metal sheet 39 except that the overcoat coating film was formed on base sheet 4 instead of on base sheet 3. Additionally, coated metal sheet 43 was produced in the same manner as coated metal sheet 3 except that the overcoat coating film was formed on base sheet 5 instead of on base sheet 3.

[Production of Coated Metal Sheets 44 and 45]

Additionally, coated metal sheet 44 was produced in the same manner as coated metal sheet 26 except that acrylic particles 6 were used instead of acrylic particles 5 as the matting agent in the overcoat coating material. Acrylic particles 6 are a classified material or its mixture, for example, wherein R2 is 10.0 μm, and D2_(97.5) is 15.0 μm.

Additionally, coated metal sheet 45 was produced in the same manner as coated metal sheet 26 except that acrylic particles 7 were used instead of acrylic particles 5 as the matting agent in the overcoat coating material. Acrylic particles 7 are a classified material or its mixture, for example, wherein R2 is 5.0 μm, and D2_(97.5) is 7.5 μm.

[Evaluation]

Coated metal sheets 1 to 45 were each subjected to the measurement and test described below.

(1) 75° Glossiness (G75)

The specular glossiness at 75° (G75), specified by JISK5600-4-7 (ISO2813: 1994), of each of coated metal sheets 1 to 45 was measured with Gloss meter VG-2000 manufactured by NIPPON DENSHOKU INDUSTRIES CO., LTD.

(2) Coating Appearance

The appearance of the overcoat coating film of each of coated metal sheets 1 to 45 after drying was evaluated in accordance with the following criteria.

(Evaluation Criteria)

G: No abnormal glossiness and coating film defects are observed, the coating film is flat, and a matte appearance is observed. NG1: The gloss is extremely high, and no matte appearance is obtained (the glossiness is higher than 25). NG2: Foaming is observed during film coating. NG3: Streaks are observed during film coating. NG4: Concealability is lacking.

(3) Scratch Resistance

Clemens-type scratch test was conducted each on coated metal sheets 1 to 45 by using a diamond needle having a diameter of 125 μm and applying a load of 400 g, and evaluation was made in accordance with the following criteria.

(Evaluation Criteria)

G: No scratch reaching the base material (metal sheet) is observed. NG: Scratches reaching the base material (metal sheet) are observed.

(4) Processed Part Adhesiveness

Coated metal sheets 1 to 45 were each subjected to 0T bending (adhesion bending), and the 0T bended portion was subjected to cellophane tape-peeling test and evaluated in accordance with the following criteria.

(Evaluation Criteria)

G: Peeling of the coating film is not observed. NG: Peeling of the coating film is observed.

(5) Flat Portion-Corrosion Resistance

First, coated metal sheets 1 to 45 were each subjected to the xenon lamp method-accelerated weathering test specified by JIS K5600-7-7 (ISO11341: 2004) for 1,000 hours. Then, each sheet was subjected to the “neutral salt water spray cycle test” specified by JIS H8502 (so-called JASO method) for 720 hours. The above-described two tests were conducted as one cycle. Test products subjected to one cycle (corresponding to about five-year service life in actual use) and test products subjected to two cycles (corresponding to about 10-year service life) each for coated metal sheets 1 to 45 were washed with water. After observed for the presence or absence of coating film blistering at the flat portion of the coated metal sheet by visual observation and magnified observation with a loupe having a magnification of 10, the sheets were evaluated in accordance with the following criteria.

(Evaluation Criteria)

A: No blistering is observed. B: Slightly subtle blistering is observed by magnified observation, but no blistering is visually observed. C: Blistering is visually observed.

The base sheet type, the gloss adjusting agent type, the matting agent type, R1, R2, D1_(97.5), D2_(97.5), Ru, the overcoat coating film resin type, T, the content of the gloss adjusting agent, the content of the matting agent, the value of D1_(97.5)/T, the value of D2_(97.5)/T, the value of Ru/T, and Example/Comparative Example of coated metal sheets 1 to 45 are shown in Table 1 and Table 2. The evaluation results of coated metal sheets 1 to 45 are also shown in Table 3 and Table 4.

TABLE 1 Matting agent Primary particles/ Overcoat Gloss adjusting agent Micro- Base Resin T R1 D1_(97.5) Ru Content D1_(97.5)/ Ru/ R2 D2_(97.5) Content D2_(97.5)/ porous No. sheet type (μm) Type (μm) (μm) (μm) (vol %) T T Type (μm) (μm) (vol %) T particles Category 1 3 PE 15 Silica 3.0 6.1 12.0 5 0.4 0.8 Acrylic 35 50 5 3.3 Primary Example 1 1 particles 2 3 PE 13 Silica 3.0 6.1 12.0 5 0.5 0.9 Acrylic 35 50 5 3.9 Primary Example 1 1 particles 3 3 PE 10 Silica 3.0 6.1 12.0 5 0.6 1.2 Acrylic 35 50 5 5.0 Primary Compar- 1 1 particles ative Example 4 3 PE 22 Silica 3.0 6.1 12.0 5 0.3 0.6 Acrylic 35 50 5 2.3 Primary Compar- 1 1 particles ative Example 5 3 PE 15 Silica 8.2 10.4 18.8 5 0.69 1.25 Acrylic 35 50 5 3.3 Primary Compar- 2 1 particles ative Example 6 3 PE 13 Silica 5.5 9.6 10.8 5 0.74 0.8 Acrylic 35 50 5 3.9 Primary Compar- 3 1 particles ative Example 7 3 PE 15 Silica 3.7 5.4 7.0 5 0.4 0.5 Acrylic 35 50 5 3.3 Primary Example 4 1 particles 8 3 PE 15 Silica 0.7 1.4 2.0 5 0.1 0.1 Acrylic 35 50 5 3.3 Primary Compar- 5 1 particles ative Example 9 3 PE 15 Silica 3.0 6.1 12.0 0.1 0.4 0.8 Acrylic 35 50 5 3.3 Primary Compar- 1 1 particles ative Example 10 3 PE 15 Silica 3.0 6.1 12.0 13 0.4 0.8 Acrylic 35 50 5 3.3 Primary Example 1 1 particles 11 3 PE 15 Silica 3.0 6.1 12.0 20 0.4 0.8 Acrylic 35 50 5 3.3 Primary Compar- 1 1 particles ative Example 12 3 PE 15 Silica 3.0 6.1 12.0 5 0.4 0.8 Acrylic 10 15 5 1.0 Primary Compar- 1 2 particles ative Example 13 3 PE 15 Silica 3.0 6.1 12.0 5 0.4 0.8 Acrylic 80 120 5 8.0 Primary Compar- 1 3 particles ative Example 14 3 PE 15 Silica 3.0 6.1 12.0 5 0.4 0.8 PAN1 10.7 33 5 2.2 Micro- Compar- 1 porous ative particles Example 15 3 PE 15 Silica 3.0 6.1 12.0 5 0.4 0.8 Acrylic 60 70 5 4.7 Primary Example 1 4 particles 16 3 PE 15 Silica 3.0 6.1 12.0 5 0.4 0.8 Acrylic 35 50 0.1 3.3 Primary Compar- 1 1 particles ative Example 17 3 PE 15 Silica 3.0 6.1 12.0 5 0.4 0.8 Acrylic 35 50 13 3.3 Primary Example 1 1 particles 18 3 PE 15 Silica 3.0 6.1 12.0 5 0.4 0.8 Acrylic 35 50 20 3.3 Primary Compar- 1 1 particles ative Example 19 5 PE 2.2 Silica 1.0 1.4 1.5 5 0.64 0.68 Acrylic 10 15 5 6.8 Primary Compar- 17 2 particles ative Example 20 5 PE 3 Silica 1.0 2.0 2.6 5 0.67 0.9 Acrylic 10 15 5 5 Primary Example 18 2 particles 21 3 PE 20 Silica 3.0 6.1 12.0 5 0.3 0.6 Acrylic 35 50 5 2.5 Primary Example 1 1 particles 22 5 PE 15 Silica 3.0 6.1 12.0 0.01 0.4 0.8 Acrylic 35 50 5 3.3 Primary Example 1 1 particles 23 5 PE 15 Silica 3.0 6.1 12.0 0.0005 0.4 0.8 Acrylic 35 50 5 3.3 Primary Compar- 1 1 particles ative Example

TABLE 2 Matting agent Gloss adjusting agent Primary Con- particles/ Overcoat tent Micro- Base Resin T R1 D1_(97.5) Ru (vol D1_(97.5)/ Ru/ R2 D2_(97.5) Content D2_(97.5)/ porous No. sheet type (μm) Type (μm) (μm) (μm) %) T T Type (μm) (μm) (vol %) T particles Category 24 5 PE 15 Silica 1 3.0 6.1 12.0 15 0.4 0.8 Acrylic 35 50 5 3.3 Primary Example 1 particles 25 5 PE 15 Silica 1 3.0 6.1 12.0 16 0.4 0.8 Acrylic 35 50 5 3.3 Primary Compar- 1 particles ative Example 26 5 PE 15 Silica 1 3.0 6.1 12.0 5 0.4 0.8 Acrylic 5 7.2 5 0.48 Primary Compar- 5 particles ative Example 27 5 PE 15 Silica 1 3.0 6.1 12.0 5 0.4 0.8 Acrylic 35 50 0.01 3.3 Primary Example 1 particles 28 5 PE 15 Silica 1 3.0 6.1 12.0 5 0.4 0.8 Acrylic 35 50 0.0005 3.3 Primary Compar- 1 particles ative Example 29 5 PE 15 Silica 1 3.0 6.1 12.0 5 0.4 0.8 Acrylic 35 50 15 3.3 Primary Example 1 particles 30 5 PE 15 Silica 1 3.0 6.1 12.0 5 0.4 0.8 Acrylic 35 50 16 3.3 Primary Compar- 1 particles ative Example 31 1 PE 15 Silica 1 3.0 6.1 12.0 5 0.4 0.8 Acrylic 35 50 5 3.3 Primary Example 1 particles 32 2 PE 15 Silica 1 3.0 6.1 12.0 5 0.4 0.8 Acrylic 35 50 5 3.3 Primary Example 1 particles 33 4 PE 15 Silica 1 3.0 6.1 12.0 5 0.4 0.8 Acrylic 35 50 5 3.3 Primary Example 1 particles 34 3 PE 15 Silica 1 3.0 6.1 12.0 5 0.4 0.8 Acrylic 35 50 5 3.3 Primary Example 1 particles 35 3 PE 15 Silica 1 3.0 6.1 12.0 5 0.4 0.8 Acrylic 35 50 5 3.3 Primary Example 1 particles 36 3 PE 15 PAN2 5.0 7.6 9.5 5 0.5 0.6 Acrylic 35 50 5 3.3 Primary Example 1 particles 37 3 PE 15 CaCPC 5.0 7.6 9.5 5 0.5 0.6 Acrylic 35 50 5 3.3 Primary Example 1 particles 38 3 PE 15 Silica 6 5.0 7.6 14.0 5 0.5 0.9 Acrylic 35 50 5 3.3 Primary Example 1 particles 39 3 PE 15 Silica 7 7.5 9.2 14.8 5 0.6 1.0 Acrylic 35 50 5 3.3 Primary Example 1 particles 40 3 PE 15 Silica 1 3.0 6.1 12.0 5 0.4 0.8 Glass 20 30 5 2.0 Primary Example particles 41 4 PE 15 Silica 6 5.0 7.6 14.0 5 0.5 0.9 Acrylic 35 50 5 3.3 Primary Example 1 particles 42 4 PE 15 Silica 7 7.5 9.2 14.8 5 0.6 1.0 Acrylic 35 50 5 3.3 Primary Example 1 particles 43 5 PE 10 Silica 1 3.0 6.1 12.0 5 0.6 1.2 Acrylic 35 50 5 5.0 Primary Example 1 particles 44 5 PE 15 Silica 1 3.0 6.1 12.0 5 0.4 0.8 Acrylic 10 15 5 1.0 Primary Example 6 particles 45 5 PE 15 Silica 1 3.0 6.1 12.0 5 0.4 0.8 Acrylic 5 7.5 5 0.5 Primary Example 7 particles

TABLE 3 Flat portion- Processed corrosion Coating Scratch part resistance appear- resis- adhe- 1 2 No. G75 ance tance siveness cycle cycle Category 1 18 G G G A A Example 2 15 G G G A A Example 3 14 G NG G — — Comparative Example 4 24 NG2 G G — — Comparative Example 5 12 G G G C C Comparative Example 6 19 G G G C C Comparative Example 7 15 G G G A B Example 8 29 NG1 G G — — Comparative Example 9 30 NG1 G G — — Comparative Example 10 7 G G G A A Example 11 5 G G NG — — Comparative Example 12 32 NG1 NG G — — Comparative Example 13 3 NG3 G G — — Comparative Example 14 21 G G G C C Comparative Example 15 5 G G G A A Example 16 51 NG1 NG G — — Comparative Example 17 14 G G G A A Example 18 3 G G NG — — Comparative Example 19 14 NG4 NG G — — Comparative Example 20 3 G G G B B Example 21 25 G G G A A Example 22 25 G G G A A Example 23 30 NG1 G G — — Comparative Example

TABLE 4 Flat portion- Processed corrosion Coating Scratch part resistance appear- resis- adhe- 1 2 Category No. G75 ance tance siveness cycle cycle 24 7 G G G A A Example 25 5 G G NG — — Comparative Example 26 32 NG1 NG G — — Comparative Example 27 24 G G G A A Example 28 51 NG1 NG G — — Comparative Example 29 14 G G G A A Example 30 3 G G NG — — Comparative Example 31 16 G G G A B Example 32 18 G G G A B Example 33 17 G G G A A Example 34 15 G G G A A Example 35 10 G G G A A Example 36 12 G G G A A Example 37 12 G G G A A Example 38 19 G G G A A Example 39 16 G G G A A Example 40 23 G G G A A Example 41 19 G G G A A Example 42 16 G G G A A Example 43 10 G G G A A Example 44 23 G G G A A Example 45 25 G G G A A Example

(6) Flat Portion-Corrosion Resistance

Coated metal sheets 1, 34, 42, and 43 were each subjected to up to three cycles of the aforementioned test according to flat portion-corrosion resistance (corresponding to about 15-year service life in actual use), and test products subjected to three cycles were each washed with water. After observed for the presence or absence of coating film blistering at the flat portion of the coated metal sheet by visual observation and magnified observation with a loupe having a magnification of 10, the sheets were evaluated in accordance with the aforementioned criteria. The results are shown in Table 5.

TABLE 5 Flat portion-corrosion resistance No. 1 cycle 2 cycle 3 cycle Category  1 A A B Example 34 A A A Example 42 A A A Example 43 A A A Example

Reference Experiment 1

Particles having a particle diameter R1′ of 0.7T μm (T=15 μm) or more were removed from silica particles 1 to obtain silica particles 1 substantially containing no particles of 10.5 μm or more. These particles are referred to as silica particles 8. Then, coated metal sheet 46 was produced in the same manner as coated metal sheet 1 except that silica particles 8 were used instead of silica particles 1 as the gloss adjusting agent in the overcoat coating material.

Additionally, particles having a particle diameter R1′ of 0.8T μm (12.0 μm) or more were removed to separately provide silica particles A substantially containing no particles of 12.0 μm or more. Into 97.5 parts by volume of silica particles 8, 2.5 parts by volume of silica particles A was mixed to obtain silica particles composed of 97.5 parts by volume of silica particles 8 of 0.7T or less and 2.5 parts by volume of silica particles A of 0.8T or less (content ratio: 97.5/2.5). These particles are referred to as silica particles 9. Then, coated metal sheet 47 was produced in the same manner as coated metal sheet 1 except that silica particles 9 were used instead of silica particles 1 as the gloss adjusting agent in the overcoat coating material.

Additionally, particles having a particle diameter R1′ of 0.9T μm (13.5 μm) or more were removed to separately provide silica particles B substantially containing no particles of 13.5 μm or more. Into 97.5 parts by volume of silica particles 8, 2.5 parts by volume of silica particles B was mixed to obtain silica particles composed of 97.5 parts by volume of silica particles 8 of 0.7T or less and 2.5 parts by volume of silica particles B of 0.9T or less. These particles are referred to as silica particles 10. Then, coated metal sheet 48 was produced in the same manner as coated metal sheet 1 except that silica particles 10 were used instead of silica particles 1 as the gloss adjusting agent in the overcoat coating material.

Additionally, particles having a particle diameter R1′ of 1.0T μm (15.0 μm) or more were removed to separately provide silica particles C substantially containing no particles of 15.0 μm or more. Into 97.5 parts by volume of silica particles 8, 2.5 parts by volume of silica particles C was mixed to obtain silica particles composed of 97.5 parts by volume of silica particles 8 of 0.7T or less and 2.5 parts by volume of silica particles C of 1.0T or less. These particles are referred to as silica particles 11. Then, coated metal sheet 49 was produced in the same manner as coated metal sheet 1 except that silica particles 11 were used instead of silica particles 1 as the gloss adjusting agent in the overcoat coating material.

Additionally, particles having a particle diameter R1′ of 1.1T μm (16.5 μm) or more were removed to separately provide silica particles D substantially containing no particles of 16.5 μm or more. Into 97.5 parts by volume of silica particles 8, 2.5 parts by volume of silica particles D was mixed to obtain silica particles composed of 97.5 parts by volume of silica particles 8 of 0.7T or less and 2.5 parts by volume of silica particles D of 1.1T or less. These particles are referred to as silica particles 12. Then, coated metal sheet 50 was produced in the same manner as coated metal sheet 1 except that silica particles 12 were used instead of silica particles 1 as the gloss adjusting agent in the overcoat coating material.

Additionally, particles having a particle diameter R1′ of 1.2T μm (18.0 μm) or more were removed to separately provide silica particles E substantially containing no particles of 18.0 μm or more. Into 97.5 parts by volume of silica particles 8, 2.5 parts by volume of silica particles E was mixed to obtain silica particles composed of 97.5 parts by volume of silica particles 8 of 0.7T or less and 2.5 parts by volume of silica particles E of 1.2T or less. These particles are referred to as silica particles 13. Then, coated metal sheet 51 was produced in the same manner as coated metal sheet 1 except that silica particles 13 were used instead of silica particles 1 as the gloss adjusting agent in the overcoat coating material.

Additionally, particles having a particle diameter R1′ of 1.3T μm (19.5 μm) or more were removed to separately provide silica particles F substantially containing no particles of 19.5 μm or more. Into 97.5 parts by volume of silica particles 8, 2.5 parts by volume of silica particles F was mixed to obtain silica particles composed of 97.5 parts by volume of silica particles 8 of 0.7T or less and 2.5 parts by volume of silica particles F of 1.3T or less. These particles are referred to as silica particles 14. Then, coated metal sheet 52 was produced in the same manner as coated metal sheet 1 except that silica particles 14 were used instead of silica particles 1 as the gloss adjusting agent in the overcoat coating material.

Coated metal sheets 46 to 52 were evaluated for flat portion-corrosion resistance in accordance with the aforementioned method. The base sheet type, the gloss adjusting agent type, the matting agent type, R1, R2, D1_(97.5), D2_(97.5), the cut value, the particle diameter R1′ of the main component of the silica particles added, the overcoat coating film resin type, T, the content of the gloss adjusting agent, the content of the matting agent, the content ratio of two types of silica particles, and evaluation results of flat portion-corrosion resistance of coated metal sheets 46 to 52 are shown in Table 6.

TABLE 6 Matting agent Flat Primary portion- Gloss adjusting agent Con- particles/ corrosion Overcoat Cut tent Micro- resistance Base Resin T R1 D1_(97.5) value Content R2 D2_(97.5) (vol D2_(97.5)/ porous 1 2 No. sheet type (μm) Type (μm) (μm) (μm) R1′ ratio Type (μm) (μm) %) T particles cycle cycle 46 3 PE 15 Silica 3.0 6.1 10.5 — 100/0  Acrylic 35 50 5 3.3 Primary A A 8 1 particles 47 3 PE 15 Silica 3.0 6.1 10.5 12.0 97.5/2.5 Acrylic 35 50 5 3.3 Primary A B 9 1 particles 48 3 PE 15 Silica 3.0 6.1 10.5 13.5 97.5/2.5 Acrylic 35 50 5 3.3 Primary B B 10 1 particles 49 3 PE 15 Silica 3.0 6.1 10.5 15.0 97.5/2.5 Acrylic 35 50 5 3.3 Primary B B 11 1 particles 50 3 PE 15 Silica 3.0 6.1 10.5 16.5 97.5/2.5 Acrylic 35 50 5 3.3 Primary B B 12 1 particles 51 3 PE 15 Silica 3.0 6.1 10.5 18.0 97.5/2.5 Acrylic 35 50 5 3.3 Primary B B 13 1 particles 52 3 PE 15 Silica 3.0 6.1 10.5 19.5 97.5/2.5 Acrylic 35 50 5 3.3 Primary B C 14 1 particles

Reference Experiment 2

Silica particles composed of 97.0 parts by volume of silica particles 8 of 0.7T or less and 3.0 parts by volume of silica particles E of 1.2T or less were obtained by changing the content ratio between silica particles 8 and silica particles E in silica particles 13. These particles are referred to as silica particles 15. Then, coated metal sheet 53 was produced in the same manner as coated metal sheet 1 except that silica particles 15 were used instead of silica particles 1 as the gloss adjusting agent in the overcoat coating material.

Additionally, silica particles composed of 96.5 parts by volume of silica particles 8 of 0.7T or less and 3.5 parts by volume of silica particles E of 1.2T or less were obtained by changing the content ratio between silica particles 8 and silica particles E in silica particles 13. These particles are referred to as silica particles 16. Then, coated metal sheet 54 was produced in the same manner as coated metal sheet 1 except that silica particles 16 were used instead of silica particles 1 as the gloss adjusting agent in the overcoat coating material.

Coated metal sheets 53 and 54 were evaluated for flat portion-corrosion resistance in accordance with the aforementioned two-cycle method. The base sheet type, the gloss adjusting agent type, the matting agent type, R1, R2, D1_(97.5), D2_(97.5), the cut value, the particle diameter R1′ of the main component of the silica particles added, the overcoat coating film resin type, T, the content of the gloss adjusting agent, the content of the matting agent, the content ratio of two types of silica particles, and evaluation results of flat portion-corrosion resistance of coated metal sheets 51, 53, and 54 are shown in Table 7.

TABLE 7 Matting agent Flat Primary portion- Gloss adjusting agent Con- particles/ corrosion Overcoat Cut tent Micro- resistance Base Resin T R1 D1_(97.5) value Content R2 D2_(97.5) (vol D2_(97.5)/ porous 1 2 No. sheet type (μm) Type (μm) (μm) (μm) R1′ ratio Type (μm) (μm) %) T particles cycle cycle 51 3 PE 15 Silica 3.0 6.1 10.5 18.0 97.5/2.5 Acrylic 35 50 5 3.3 Primary B B 13 1 particles 53 3 PE 15 Silica 3.0 6.1 10.5 18.0 97.0/3.0 Acrylic 35 50 5 3.3 Primary B C 15 1 particles 54 3 PE 15 Silica 3.0 6.1 10.5 18.0 96.5/3.5 Acrylic 35 50 5 3.3 Primary B C 16 1 particles

Reference Experiment 3

Coated metal sheet 55 was produced in the same manner as coated metal sheet 52 except that the overcoat coating material for coated metal sheet 52 was treated with a roller mill under conditions for pulverizing silica particles F before the matting agent was blended. Then, coated metal sheet 55 was evaluated for flat portion-corrosion resistance in accordance with the aforementioned method, and graded B both in the one-cycle test and the two-cycle test.

As clear from Table 1 to Table 4, coated metal sheets 1, 2, 7, 10, 15, 17, 20 to 22, 24, 27, 29, and 31 to 45 all have designability of a matte gloss, have sufficient processed-part adhesiveness and scratch resistance, and additionally have flat portion-corrosion resistance corresponding to 10 years of actual use.

In contrast, coated metal sheets 5, 6, and 14 had insufficient flat portion-corrosion resistance. It is conceivable that coated metal sheets 5 and 6 had insufficient flat portion-corrosion resistance because the gloss adjusting agent was exposed from the overcoat coating film during the resistance test due to optical degradation of the overcoat coating film and that coated metal sheet 14 had insufficient flat portion-corrosion resistance because the matting agent was exposed from the overcoat coating film during the resistance test due to optical degradation of the overcoat coating film.

Additionally, the coated metal sheet 8 has an extremely high gloss, and the intended designability (matte appearance) could not achieved. It is conceivable that this was because the particle diameter of the gloss adjusting agent was extremely small.

Additionally, in coated metal sheet 4, foaming occurred on coating of the overcoat coating film, and the intended designability could not achieved. Thus, it was determined that coated metal sheet 4 did not deserve to be subject to evaluation test of flat portion-corrosion resistance, and the evaluation test was not conducted. It is conceivable that the reason why the above-described designability was not obtained is that the film thickness of the overcoat coating film was extremely thick.

Additionally, in coated metal sheet 13, streaks occurred on coating of the overcoat coating film, and the intended designability could not achieved. Thus, it was not possible to conduct evaluation test of flat portion-corrosion resistance. It is conceivable that this this was because D2_(97.5)/T was extremely large.

Additionally, coated metal sheet 19 lacked concealability. In other words, the visibility of the overcoat coating film was developed only to the extent where the substrate of the overcoat coating film (intercoat coating film) was visually observed, and the intended designability could not achieved. Thus, it was determined that coated metal sheet 4 did not deserve to be subject to evaluation test of flat portion-corrosion resistance, and the evaluation test was not conducted. It is conceivable that the reason why the above-described concealability was insufficient is that the film thickness of the overcoat coating film was extremely thin as well as the particle diameter of the gloss adjusting agent was extremely small.

Furthermore, the coated metal sheets 9, 12, 16, 23, 26, and 28 had an extremely high gloss, and the intended designability (matte feeling) could not achieved. It is conceivable that coated metal sheets 9 and 23 had an extremely high gloss because the content of the gloss adjusting agent was too low to adjust the gloss, that coated metal sheets 16 and 28 had an extremely high gloss because the content of the matting agent was too low to adjust the gloss, and that coated metal sheets 12 and 26 had an extremely high gloss because D2_(97.5)/T was extremely small.

Alternatively, coated metal sheets 11, 18, 25, and 30 had insufficient processed-part adhesiveness. Thus, it was not possible to conduct evaluation test of flat portion-corrosion resistance. It is conceivable that coated metal sheets 11 and 25 had insufficient processed-part adhesiveness because the content of the gloss adjusting agent in the overcoat coating film was extremely high, and that coated metal sheets 18 and 30 had insufficient processed-part adhesiveness because the content of the matting agent in the overcoat coating film was extremely high.

Alternatively, coated metal sheets 3, 12, 16, 19, 26, and 28 had insufficient scratch resistance. Thus, it was not possible to conduct evaluation test of flat portion-corrosion resistance. It is conceivable that coated metal sheets 3 and 19 had insufficient scratch resistance because the film thickness of the overcoat coating film was extremely small, that coated metal sheets 12 and 26 had insufficient scratch resistance because D2_(97.5)/T was extremely small, and that coated metal sheets 16 and 28 had insufficient scratch resistance because the content of the matting agent was extremely low.

Additionally, coated metal sheets 31 to 33 and 41 to 43 all exhibited the intended designability (matte) irrespective of the type of the base sheet as well as had sufficient processed part-adhesiveness, scratch resistance, and flat portion-corrosion resistance. It is conceivable that this is because flat portion-corrosion resistance is provided by the overcoat coating film.

Additionally, coated metal sheet 34 and 35 both exhibited the intended designability (matte) irrespective of the type of the overcoat coating film resin as well as had sufficient processed part-adhesiveness, scratch resistance, and flat portion-corrosion resistance. It is conceivable that this is because a resin having sufficient durability to be used for the overcoat coating film would exhibit flat portion-corrosion irrespective of the type of the resin constituting the overcoat coating film resistance.

Additionally, coated metal sheets 36 to 39 all exhibited the intended designability (matte) irrespective of the type of the gloss adjusting agent as well as had sufficient processed part-adhesiveness, scratch resistance, and flat portion-corrosion resistance. It is conceivable that this is because even particles having micropores, if not exposed from the surface of the overcoat coating film, would exhibit sufficient flat portion-corrosion resistance, whether the particles are inorganic particles or organic particles.

Coated metal sheets 40, 44 and 45 also exhibited the intended designability (matte) irrespective of the type of the matting agent as well as had sufficient processed part-adhesiveness, scratch resistance, and flat portion-corrosion resistance. It is conceivable that this is because primary particles would exhibit sufficient flat portion-corrosion resistance, whether the particles are inorganic particles or organic particles.

Also as clear from Table 5, coated metal sheets 34, 42, and 43 all maintain flat portion-corrosion resistance for a period longer than coated metal sheet 1. It is conceivable that this is because base sheet 4 in coated metal sheets 34, 42, and 43, which contains a chromate-based anti-rust pigment in the undercoat coating film and of which plated steel sheet has been subjected to chromate anti-rust treatment, has higher corrosion resistance than that of base sheet 1 in coated metal sheet 1.

Also it is obvious from Table 6 and Table 7, it can be seen that the gloss adjusting agent has no substantially adverse influence on the flat portion-corrosion resistance of the coated metal sheet even if particles larger than 0.7T are contained, provided that the content of the particles is 2.5 vol % or less based on the total and that the particle diameter of the particles is 1.2 times (1.2T) or less the film thickness of the overcoat coating film. It is conceivable that this is because particles slightly larger than the film thickness T of the overcoat coating film are likely to be oriented such that their long diameter is along the direction in which the overcoat coating material is applied and, if in a small amount, will be sufficiently and continuously covered with the resin of the overcoat coating film for the intended use period.

The gloss adjusting agent may also contain large particles which may be detected in a position deviating from its particle size distribution (coarse particles), although in a small amount. It is conceivable that such coarse particles, as clear from Table 6, are exposed from the overcoat coating film in durable use to cause impairment in the flat portion-corrosion resistance of the coated metal sheet. However, when the overcoat coating material containing the above-described coarse particles is subjected to an appropriate pulverizing step, a coated metal sheet having sufficient flat portion-corrosion resistance can be obtained. It is conceivable that this is because the above-described coarse particles are finely pulverized in the overcoat coating material to a degree enough for the coated metal sheet to exhibit the intended portion-corrosion resistance.

This application is entitled to and claims the benefit of Japanese Patent Application 2014-111308 filed on May 29, 2014, and Japanese Patent Application 2014-164258 filed on Aug. 12, 2014, the disclosure of which including the specification, drawings and abstract is incorporated herein by reference in its entirety.

INDUSTRIAL APPLICABILITY

In the coated metal sheet according to the present invention, reduction in the corrosion resistance in the flat portion, attributable to exposure, collapse and fall-off of the gloss adjusting agent and exposure, cracking, collapse, and fall-off of the matting agent from the overcoat coating film, is prevented. Thus, a coated metal sheet that exhibits the intended appearance and corrosion resistance for a long period can be obtained, even if used in an exterior application for a long period. Accordingly, the present invention is expected to further prolong the life of coated metal sheets for exterior use and to further enhance its usage. 

1. A coated metal sheet comprising: a metal sheet, and an overcoat coating film to be disposed on the metal sheet, wherein the overcoat coating film comprises a gloss adjusting agent which is particles having micropores and a matting agent which is primary particles, wherein a content of the gloss adjusting agent in the overcoat coating film is from 0.2 to 15 vol %, wherein a content of the matting agent in the overcoat coating film is from 0.2 to 15 vol %, and wherein the coated metal sheet satisfies the following equations: D1_(97.5) /T≦0.7 Ru≦1.2T R≧1.0 2.0≦D2_(97.5) /T≦7.0 13≦T≦20 wherein R (μm) is a number average particle diameter of the gloss adjusting agent, T (μm) is a film thickness of the overcoat coating film, D1_(97.5) (μm) is a 97.5% particle diameter in an accumulated particle size distribution of the gloss adjusting agent based on the number of particles, D2_(97.5) (μm) is a 97.5% particle diameter in an accumulated particle size distribution of the matting agent based on the number of particles, and Ru (μm) is an upper limit particle diameter in a number particle size distribution of the gloss adjusting agent.
 2. A coated metal sheet comprising: a metal sheet, an intercoat coating film to be disposed on the metal sheet, and an overcoat coating film to be disposed on the intercoat coating film, wherein the overcoat coating film comprises a gloss adjusting agent which is particles having micropores and a matting agent which is primary particles, wherein a content of the gloss adjusting agent in the overcoat coating film is from 0.01 to 15 vol %, wherein a content of the matting agent in the overcoat coating film is from 0.01 to 15 vol %, and wherein the coated metal sheet satisfies the following equations: D1_(97.5) /T≦0.7 Ru≦1.2T R≧1.0 0.5≦D2_(97.5) /T≦7.0 3≦T≦20 wherein R (μm) is a number average particle diameter of the gloss adjusting agent, T (μm) is a film thickness of the overcoat coating film, D1_(97.5) (μm) is a 97.5% particle diameter in an accumulated particle size distribution of the gloss adjusting agent based on the number of particles, D2_(97.5) (μm) is a 97.5% particle diameter in an accumulated particle size distribution of the matting agent based on the number of particles, and Ru (μm) is an upper limit particle diameter in a number particle size distribution of the gloss adjusting agent.
 3. The coated metal sheet according to claim 1, further comprising an undercoat coating film between the metal sheet and the overcoat coating film.
 4. The coated metal sheet according to claim 2, further comprising an undercoat coating film between the metal sheet and the intercoat coating film.
 5. The coated metal sheet according to claim 1, wherein the Ru is less than T.
 6. The coated metal sheet according to claim 1, wherein the metal sheet has been subjected to non-chromate anti-rust treatment, and the coated metal sheet is chromate-free.
 7. The coated metal sheet according to claim 1, wherein the metal sheet has been subjected to chromate anti-rust treatment.
 8. The coated metal sheet according to claim 1, wherein the gloss adjusting agent is silica particles.
 9. The coated metal sheet according to claim 1, having a glossiness at 75° is 1 to
 25. 10. The coated metal sheet according to claim 1, being a coated metal sheet for exterior use.
 11. An exterior building material composed of the coated metal sheet according to claim
 1. 12. A method for producing a coated metal sheet comprising a metal sheet and an overcoat coating film to be disposed on the metal sheet, comprising the steps of: applying an overcoat coating material containing a resin, a gloss adjusting agent, and a matting agent onto the metal sheet; and curing the coating film of the overcoat coating material to form the overcoat coating film; wherein a content of the gloss adjusting agent in the overcoat coating film is from 0.2 to 15 vol %, and a content of the matting agent in the overcoat coating film is from 0.2 to 15 vol %, wherein the gloss adjusting agent is particles having micropores, and the matting agent is primary particles, and wherein the gloss adjusting agent and the matting agent which satisfy the following equations are employed: D1_(97.5) /T≦0.7 Ru≦1.2T R≧1.0 2.0≦D2_(97.5) /T≦7.0 13≦T≦20 wherein R (μm) is a number average particle diameter of the gloss adjusting agent, T (μm) is a film thickness of the overcoat coating film, D1_(97.5) (μm) is a 97.5% particle diameter in an accumulated particle size distribution of the gloss adjusting agent based on the number of particles, D2_(97.5) (μm) is a 97.5% particle diameter in an accumulated particle size distribution of the matting agent based on the number of particles, and Ru (μm) is an upper limit particle diameter in a number particle size distribution of the gloss adjusting agent.
 13. A method for producing a coated metal sheet comprising a metal sheet and an overcoat coating film to be disposed on the metal sheet, comprising the steps of: applying an overcoat coating material containing a resin, a gloss adjusting agent, and a matting agent onto the metal sheet; and curing the coating film of the overcoat coating material to form the overcoat coating film; wherein a content of the gloss adjusting agent in the overcoat coating film is from 0.01 to 15 vol %, and a content of the matting agent in the overcoat coating film is from 0.01 to 15 vol %, wherein the gloss adjusting agent is particles having micropores, and the matting agent is primary particles, and wherein the gloss adjusting agent and the matting agent which satisfy the following equations are employed: D1_(97.5) /T≦0.7 Ru≦1.2T R≧1.0 0.5≦D2_(97.5) /T≦7.0 3≦T≦20 wherein R (μm) is a number average particle diameter of the gloss adjusting agent, T (μm) is a film thickness of the overcoat coating film, D1_(97.5) (μm) is a 97.5% particle diameter in an accumulated particle size distribution of the gloss adjusting agent based on the number of particles, D2_(97.5) (μm) is a 97.5% particle diameter in an accumulated particle size distribution of the matting agent based on the number of particles, and Ru (μm) is an upper limit particle diameter in a number particle size distribution of the gloss adjusting agent.
 14. The method for producing a coated metal sheet according to claim 12, wherein the overcoat coating material has been subjected to treatment for pulverizing the particles in the overcoat coating material.
 15. The method for producing a coated metal sheet according to claim 13, wherein the overcoat coating material has been subjected to treatment for pulverizing the particles in the overcoat coating material.
 16. The coated metal sheet according to claim 2, wherein the Ru is less than T.
 17. The coated metal sheet according to claim 2, wherein the metal sheet has been subjected to non-chromate anti-rust treatment, and the coated metal sheet is chromate-free.
 18. The coated metal sheet according to claim 2, wherein the metal sheet has been subjected to chromate anti-rust treatment.
 19. The coated metal sheet according to claim 2, wherein the gloss adjusting agent is silica particles.
 20. The coated metal sheet according to claim 2, having a glossiness at 75° is 1 to
 25. 21. The coated metal sheet according to claim 2, being a coated metal sheet for exterior use.
 22. An exterior building material composed of the coated metal sheet according to claim
 2. 